Create a simple version of the board game:   Mastermind.

Task
Mastermind
You are encouraged to solve this task according to the task description, using any language you may know.

It must be possible to:

  •   choose the number of colors will be used in the game (2 - 20)
  •   choose the color code length (4 - 10)
  •   choose the maximum number of guesses the player has (7 - 20)
  •   choose whether or not colors may be repeated in the code


The (computer program) game should display all the player guesses and the results of that guess.

Display (just an idea):

Feature Graphic Version Text Version
Player guess Colored circles Alphabet letters
Correct color & position Black circle X
Correct color White circle O
None Gray circle -


A text version example:       1.   ADEF   -   XXO-
Translates to:
the first guess;
the four colors (ADEF);
result:

two correct colors and spot,
one correct color/wrong spot, one color isn't in the code.

Happy coding!


Related tasks



11l

Translation of: Python
F encode(correct, guess)
   [String] output_arr

   L(i) 0 .< correct.len
      output_arr [+]= I guess[i] == correct[i] {‘X’} E I guess[i] C correct {‘O’} E ‘-’

   R output_arr

F safe_int_input(prompt, min_val, max_val)
   L
      V user_input_str = input(prompt)

      X.try
         V user_input = Int(user_input_str)
         I user_input C min_val .. max_val
            R user_input
      X.catch ValueError
         L.continue

F play_game()
   print(‘Welcome to Mastermind.’)
   print(‘You will need to guess a random code.’)
   print(‘For each guess, you will receive a hint.’)
   print(‘In this hint, X denotes a correct letter, and O a letter in the original string but in a different position.’)
   print()

   V number_of_letters = safe_int_input(‘Select a number of possible letters for the code (2-20): ’, 2, 20)
   V code_length = safe_int_input(‘Select a length for the code (4-10): ’, 4, 10)

   V letters = ‘ABCDEFGHIJKLMNOPQRST’[0 .< number_of_letters]
   V code = ‘’
   L 0 .< code_length
      code ‘’= random:choice(letters)
   [String] guesses

   L
      print()
      V guess = input(‘Enter a guess of length #. (#.): ’.format(code_length, letters)).uppercase()

      I guess.len != code_length | any(guess.map(char -> char !C @letters))
         L.continue
      E I guess == code
         print("\nYour guess "guess‘ was correct!’)
         L.break
      E
         guesses.append(‘#.: #. => #.’.format(guesses.len + 1, Array(guess).join(‘ ’), encode(code, guess).join(‘ ’)))

      L(i_guess) guesses
         print(‘------------------------------------’)
         print(i_guess)
      print(‘------------------------------------’)

play_game()
Output:
Welcome to Mastermind.
You will need to guess a random code.
For each guess, you will receive a hint.
In this hint, X denotes a correct letter, and O a letter in the original string but in a different position.

Select a number of possible letters for the code (2-20): 4
Select a length for the code (4-10): 4

Enter a guess of length 4 (ABCD): abcd
------------------------------------
1: A B C D => X X O O
------------------------------------

Enter a guess of length 4 (ABCD): abcc
------------------------------------
1: A B C D => X X O O
------------------------------------
2: A B C C => X X O X
------------------------------------

Enter a guess of length 4 (ABCD): abdc

Your guess ABDC was correct!

Action!

DEFINE MINCOLORS="2"
DEFINE MAXCOLORS="20"
DEFINE MINLENGTH="4"
DEFINE MAXLENGTH="10"
DEFINE MINGUESS="7"
DEFINE MAXGUESS="20"
TYPE Score=[BYTE spot,corr,err]
TYPE Settings=[BYTE colors,length,guesses,repeat]

PROC GetSettings(Settings POINTER s)
  CHAR ARRAY tmp(10)

  DO
    PrintF("Enter number of colors (%B-%B):",MINCOLORS,MAXCOLORS)
    s.colors=InputB()
  UNTIL s.colors>=MINCOLORS AND s.colors<=MAXCOLORS
  OD
  DO
    PrintF("Enter length of code (%B-%B):",MINLENGTH,MAXLENGTH)
    s.length=InputB()
  UNTIL s.length>=MINLENGTH AND s.length<=MAXLENGTH
  OD
  DO
    PrintF("Enter max number of guesses (%B-%B):",MINGUESS,MAXGUESS)
    s.guesses=InputB()
  UNTIL s.guesses>=MINGUESS AND s.guesses<=MAXGUESS
  OD
  IF s.colors<s.length THEN
    s.repeat=1
  ELSE
    DO
      Print("Allow repeated colors (Y/N):")
      InputS(tmp)
      IF tmp(0)=1 THEN
        IF tmp(1)='y OR tmp(1)='Y THEN
          s.repeat=1 EXIT
        ELSEIF tmp(1)='n OR tmp(1)='N THEN
          s.repeat=0 EXIT
        FI
      FI
    OD
  FI
RETURN

PROC Generate(CHAR ARRAY code Settings POINTER s)
  CHAR ARRAY col(MAXCOLORS)
  BYTE i,j,d,tmp,count

  FOR i=0 TO MAXCOLORS-1
  DO
    col(i)=i+'A
  OD
  code(0)=s.length
  count=s.colors
  FOR i=1 TO s.length
  DO
    d=Rand(count)
    code(i)=col(d)
    IF s.repeat=0 THEN
      count==-1
      col(d)=col(count)
    FI
  OD
RETURN

BYTE FUNC GetCount(CHAR ARRAY s CHAR c)
  BYTE i,count

  count=0
  FOR i=1 TO s(0)
  DO
    IF s(i)=c THEN
      count==+1
    FI
  OD
RETURN (count)

PROC CheckScore(CHAR ARRAY code,guess
  Settings POINTER s Score POINTER res)
  BYTE i,j,codeCount,guessCount

  res.spot=0
  res.corr=0
  IF guess(0)#s.length THEN
    res.err=1
    RETURN
  FI
  res.err=0

  FOR i=0 TO s.colors-1
  DO
    codeCount=GetCount(code,i+'A)
    guessCount=GetCount(guess,i+'A)
    IF codeCount<guessCount THEN
      res.corr==+codeCount
    ELSE
      res.corr==+guessCount
    FI
  OD
  FOR i=1 TO s.length
  DO
    IF guess(i)=code(i) THEN
      res.spot==+1
      res.corr==-1
    FI
  OD
RETURN

PROC ToUpper(CHAR ARRAY s)
  BYTE i,c

  IF s(0)=0 THEN RETURN FI
  FOR i=1 TO s(0)
  DO
    c=s(i)
    IF c>='a AND c<='z THEN
      s(i)=c-'a+'A
    FI
  OD
RETURN

PROC PrintScore(Score POINTER res Settings POINTER s)
  INT i

  FOR i=1 TO res.spot
  DO Put('X) OD
  FOR i=1 TO res.corr
  DO Put('O) OD
  FOR i=1 TO s.length-res.spot-res.corr
  DO Put('-) OD
RETURN

PROC Main()
  CHAR ARRAY code(MAXLENGTH+1),guess(255)
  Score res
  Settings s
  BYTE tries

  PrintE("Mastermind") PutE()
  GetSettings(s) PutE()
  Generate(code,s)
  tries=s.guesses
  PrintF("Enter your guess (%B tries):%E",tries)
  DO
    InputS(guess) ToUpper(guess)
    CheckScore(code,guess,s,res)
    Put(28) ;cursor up
    PrintF("%S -> ",guess)
    IF res.err THEN
      Print("Wrong input")
    ELSE
      PrintScore(res,s)
      IF res.spot=s.length THEN
        PutE() PutE()
        PrintE("You won!")
        EXIT
      FI
      tries==-1
      IF tries=0 THEN
        PutE() PutE()
        PrintE("You lost!")
        EXIT
      FI
    FI
    PrintF(", try again (%B tries):%E",tries)
  OD
RETURN
Output:

Screenshot from Atari 8-bit computer

Mastermind

Enter number of colors (2-20):6
Enter length of code (4-10):5
Enter max number of guesses (7-20):20
Allow repeated colors (Y/N):Y

Enter your guess (20 tries):
AAAA -> Wrong input, try again (20 tries):
AAAAA -> -----, try again (19 tries):
BBBBB -> -----, try again (18 tries):
CCCCC -> -----, try again (17 tries):
DDDDD -> XX---, try again (16 tries):
EEEEE -> X----, try again (15 tries):
DDEFF -> XXXXX

You won!

Ada

Works with: Ada version 2012
with Ada.Text_IO;
with Ada.Numerics.Discrete_Random;
with Ada.Strings.Fixed;
with Ada.Containers.Ordered_Sets;

use Ada.Strings.Fixed;

procedure MasterMind
is
   subtype Color_Number is Positive range 2 .. 20;
   subtype Code_Size is Positive range 4 .. 10;
   subtype Guesses_Number is Positive range 7 .. 20;
   subtype Color is Character range 'A' .. 'T';

   function Hint(correct, guess : in String) return String
   is
      Xs : Natural := 0;
      Os : Natural := 0;
      to_display : String(1 .. correct'Length) := (others => '-');
   begin
      for I in guess'Range loop
         if guess(I) = correct(I) then
            Xs := Xs + 1;
            to_display(I) := 'X';
         end if;
      end loop;
      for I in guess'Range loop
         if to_display(I) = '-' then
            for J in correct'Range loop
               if J /= I and to_display(J) /= 'X' and correct(J) = guess(I) then
                  Os := Os + 1;
                  exit;
               end if;
            end loop;
         end if;
      end loop;
      return Xs * 'X' & Os * 'O' & (guess'Length - Xs - Os) * '-';
   end Hint;

   generic
      type Data is (<>);
   function Input(message : in String) return Data;
   -- Input will loop until a correct value is given by the user.
   -- For each wrong input, the program will prompt the range of expected values.

   function Input(message : in String) return Data is
   begin
      loop
         Ada.Text_IO.Put(message);
         declare
            S : constant String := Ada.Text_IO.Get_Line;
         begin
            return Data'Value(S);
         exception
            when Constraint_Error =>
               Ada.Text_IO.New_Line;
               Ada.Text_IO.Put_Line("Invalid input!");
               Ada.Text_IO.Put_Line
                 ("Expected values in range:"
                  & Data'First'Img & " .." & Data'Last'Img);
               Ada.Text_IO.New_Line;
         end;
      end loop;
   end;

   function Input_Color_Number is new Input(Color_Number);
   function Input_Code_Size is new Input(Code_Size);
   function Input_Guesses_Number is new Input(Guesses_Number);
   function Input_Boolean is new Input(Boolean);

   CN : constant Color_Number := Input_Color_Number("How many colors? ");
   GN : constant Guesses_Number := Input_Guesses_Number("How many guesses? ");
   CS : constant Code_Size := Input_Code_Size("Size of the code? ");
   repeats : Boolean := Input_Boolean("With repeats? ");
   -- Not constant: if Color < Code_Size, we will have repetitions anyway.

   subtype Actual_Colors is Color range Color'First .. Color'Val(Color'Pos(Color'First) + CN - 1);
   package Actual_Colors_Sets is new Ada.Containers.Ordered_Sets(Element_Type => Actual_Colors);

   package Color_Random is new Ada.Numerics.Discrete_Random(Result_Subtype => Actual_Colors);
   generator : Color_Random.Generator;

   function Random return String
   is
      C : String(1 .. CS);
      seen : Actual_Colors_Sets.Set;
   begin
      for I in C'Range loop
         C(I) := Color_Random.Random(generator);
         while (not repeats) and seen.Contains(C(I)) loop
            C(I) := Color_Random.Random(generator);
         end loop;
         seen.Include(C(I));
      end loop;
      return C;
   end Random;

   function Get_Code return String is
   begin
      loop
         Ada.Text_IO.Put("> ");
         declare
            input : constant String := Ada.Text_IO.Get_Line;
         begin
            if input'Length /= CS then
               raise Constraint_Error;
            end if;
            for C of input loop
               if C not in Actual_Colors then
                  raise Constraint_Error;
               end if;
            end loop;
            return input;
         exception
            when Constraint_Error =>
               Ada.Text_IO.New_Line;
               Ada.Text_IO.Put_Line("Invalid input!");
               Ada.Text_IO.New_Line;
         end;
      end loop;
   end Get_Code;

   found : Boolean := False;
begin
   if (not repeats) and (CN < CS) then
      Ada.Text_IO.Put_Line("Not enough colors! Using repeats anyway.");
      repeats := True;
   end if;

   Color_Random.Reset(generator);

   declare
      answer : constant String := Random;
      previous : array(1 .. GN) of String(1 .. CS*2);
   begin
      for I in 1 .. GN loop
         declare
            guess : constant String := Get_Code;
         begin
            if guess = answer then
               Ada.Text_IO.Put_Line("You won, congratulations!");
               found := True;
            else
               previous(I) := guess & Hint(answer, guess);
               Ada.Text_IO.Put_Line(44 * '-');
               for J in 1 .. I loop
                  Ada.Text_IO.Put_Line
                    (previous(J)(1 .. CS)
                     & " => " & previous(J)(CS+1 .. previous(J)'Last));
               end loop;
               Ada.Text_IO.Put_Line(44 * '-');
               Ada.Text_IO.New_Line;
            end if;
         end;
         exit when found;
      end loop;
      if not found then
         Ada.Text_IO.Put_Line("You lost, sorry! The answer was: " & answer);
      end if;
   end;
end MasterMind;
Output:
How many colors? 9
How many guesses? 4

Invalid input!
Expected values in range: 7 .. 20

How many guesses? 20
Size of the code? 4
With repeats? False
> ABCD
--------------------------------------------
ABCD => XOO-
--------------------------------------------

> EFGH
--------------------------------------------
ABCD => XOO-
EFGH => O---
--------------------------------------------

> ABCE
--------------------------------------------
ABCD => XOO-
EFGH => O---
ABCE => XOO-
--------------------------------------------

> ABCF
--------------------------------------------
ABCD => XOO-
EFGH => O---
ABCE => XOO-
ABCF => XOO-
--------------------------------------------

> ABCG
--------------------------------------------
ABCD => XOO-
EFGH => O---
ABCE => XOO-
ABCF => XOO-
ABCG => XXOO
--------------------------------------------

> ACBG
You won, congratulations!

APL

Works with: GNU APL
#!/usr/local/bin/apl -s -f -- 

⍝ Define the alphabet
A'ABCDEFGHIJKLMNOPQRSTUVWXYZ'

⍝ Make ASCII values upper case
nAscUp c
        nc-32×(c97)(c122)


⍝ Does a list have repeated values?
rRpts l
        r(ll)≢⍳⍴l


⍝ Keyboard input using ⎕ and ⍞ doesn't work well using GNU APL in script mode,
⍝ so you kind of have to write your own.
⍝ Read a line of text from the keyboard
lReadLine up;k;z;data
        data''  csr0 ⍝ Start out with empty string and cursor at 0

        ⍝⍝⍝ Keyboard input
in:     k1⎕fio[41]1    ⍝ Read byte from stdin
handle: (k>127)/skip   ⍝ Unicode is not supported (Wumpus doesn't need it)
        (k8 127)/back ⍝ Handle backspace
        (k=10)/done    ⍝ Newline = Enter key pressed
        (k<32)/in      ⍝ For simplicity, disregard terminal control entirely

        k(AscUpup)k   ⍝ Make key uppercase if necessary 
        zk⎕fio[42]0    ⍝ Echo key to stdout
        datadata,k     ⍝ Insert key into data
        in             ⍝ Go get next key

        ⍝⍝⍝ Skip UTF-8 input (read until byte ≤ 127)
skip:   k1⎕fio[41]1  (k>127)/skip  handle
             
        ⍝⍝ Backspace
back:   (0=⍴data)/in   ⍝ If already at beginning, ignore
        zk⎕fio[42]0    ⍝ Backspace to terminal
        data¯1data    ⍝ Remove character 
        in             ⍝ Get next key
        
        ⍝⍝ We are done, return the line as text
done:   l⎕UCS data


⍝ Read a positive number from the keyboard in the range [min...max]
nmin ReadNum max;l;z
in:     lReadLine 0
        z10⎕fio[42]0
        (~l.'0123456789')/no
        ((minn)maxnl)/0
no:     'Please enter a number between ',(min),' and ',(max),': '
        in


⍝ Ask a numeric question 
nq Question lim;min;max
        (min max)lim
        q,' [',(min),'..',(max),']? '
        nmin ReadNum max


⍝ Read a choice from the keyboard
cChoice cs;ks;k;z
        ksAscUp ⎕UCS ¨cs              ⍝ User should press first letter of choice
in:     (~(kAscUp 1⎕fio[41]1)ks)/in  ⍝ Wait for user to make choice
        z(ccs[ksk])⎕fio[42]0       ⍝ Select and output correspoinding choice


⍝ Ask the user for game parameters
parmsInitGame;clrs;len;gss;rpts
        '∘∘∘ MASTERMIND ∘∘∘'  ''
        clrs'How many colors' Question 2 20
        len'Code length' Question 4 10
        gss'Maximum amount of guesses' Question 7 20
        'Allow repeated colors in code (Y/N)? '
        rpts'Yes'Choice 'Yes' 'No'
        parmsclrs len gss rpts


⍝ Generate a code.
crpts MakeCode parms;clrs;len
        (clrs len)parms
        cA[(1+rpts)(len?clrs)(?len/clrs)]


⍝ Let user make a guess and handle errors
gparms Guess code;clrs;rpts;l;right;in
        (clrs rpts num)parms
        
guess:  'Guess ',(¯2↑⍕num),': '  gReadLine 1      ⍝ Read a guess from the keyboard
        
        ⍝ Don't count obvously invalid input against the user
        ((code)≢⍴g)/len               ⍝ Length is wrong
        (~g.A[clrs])/inv            ⍝ Invalid code in input
        ((~rpts)Rpts g)/rpt           ⍝ No repeats allowed 
        
        ⍝ Give feedback
        rightg=code                    ⍝ Colors in right position
        ingcode                       ⍝ Colors not in right position
        fb(+/right)/'X'                ⍝ X = amount of matching ones
        fbfb,(+/in∧~right)/'O'         ⍝ O = amount of non-matching ones
        fbfb,(+/~in)/'-'               ⍝ - = amount of colors not in code
        ' --→ ',fb,⎕UCS 10
        0
len:    'Invalid length.'  guess
inv:    'Invalid color.'  guess
rpt:    'No repeats allowed.'  guess


⍝ Play the game
 Mastermind;clrs;len;gsmax;rpts;code;gs
        ⎕rl(2*32)/⎕ts                ⍝ initialize random seed 
        (clrs len gsmax rpts)InitGame
        coderpts MakeCode clrs len
        2 0''
        'The code consists of: ',A[clrs]
        gs0
loop:   gsgs+1 
        (gs>gsmax)/lose
        (code(clrs rpts gs)Guess code)/loop
        '○○○ Congratulations! ○○○'
        'You won in ',(gs),' guesses.'
        0
lose:   'Alas, you are out of guesses.'
        'The code was: ',code


Mastermind
)OFF

AutoHotkey

w := h := 32, maxRows := 10, numPegs := 8
ww := floor(w/2-2), hh := floor(h/2-2)
grid := [], dx := w*4.5
gosub, Decode

Gui, Font, S18, Consolas
loop, 4
{
	i := A_Index-1
	Gui, add, button, % "x" (Mod(i, 4)?"+0":"30") " y" 
					.	(Mod(i, 4)?"10" : "10") " w" w " h" h " vGoal" A_Index , ?
}

Gui, Add, Text, % "section x30 h1 0x1000 w" w*6
loop, % maxRows
{
	Gui, Font, S18, consolas
	row := maxRows - A_Index + 1
	loop 4
	{
		col := A_Index, 	i:= col-1
		Gui, add, button, % "x" (Mod(i, 4)?"+0":"s") " y" (Mod(i, 4)?"p":"+2") 
						. " w" w " h" h " vButton" row "_" col " gButton"
	}
	Gui, Font, S13, wingdings 2
	loop 2
	{
		col := A_Index, 	i:= col-1
		Gui, add, text, % "x" (Mod(i,2)?"+1":"s+" dx) " y" (Mod(i,2)?"p":"p+1")
						. " w" ww " h" hh " vKeyPeg" row "_" col, % Chr(167)
	}
	loop 2
	{
		col := A_Index+2, 	i:= col-1
		Gui, add, text, % "x" (Mod(i,2)?"+1":"s+" dx) " y" (Mod(i,2)?"p":"+1") 	
						. " w" ww " h" hh " vKeyPeg" row "_" col, % Chr(167)
	}
	Gui, Add, Text, % "section xs h1 0x1000 w" w*6 " y+4"
}
Gui, Font, S12, consolas
Gui, add, Button, % "xs y+10 gSubmit w" W*2 , Submit
Gui, add, Button, % "x+0 gResetMM w" W*2, Reset
Gui, add, Checkbox, % "x+4 vNoDup", No`nDuplicates
Gui, Font, S18
for i, v in pegs
	Gui, add, Radio, % "x" (!Mod(i-1, 4)?"10":"+10") " h" h " w" w+20 " vRadio" A_Index, % v
Gui, show
Row := 1
return
;-----------------------------------------------------------------------
GuiClose:
ExitApp
return
;-----------------------------------------------------------------------
Decode:
Gui, Submit, NoHide
pegs:=[], goal := [], usedPeg :=[]
pool := ["😺","🎃","🧨","⚽","😀","☠","👽","❄","🙉","💗"
	,"💥","🖐","🏈","🎱","👁","🗨","🤙","👄","🐶","🐴"
	,"🦢","🐍","🐞","💣","🐪","🐘","🐰","🐸","🌴","🏀"]

loop, % numPegs
{
	Random, rnd, 1, % pool.count()
	pegs[A_Index] := pool.RemoveAt(rnd)
}
i := 1
while (goal.count()<4)
{
	Random, rnd, 1, % pegs.count()
	if (NoDup && usedPeg[pegs[rnd]])
		continue
	goal[i++] := pegs[rnd]
	usedPeg[pegs[rnd]] := true
}
return
;-----------------------------------------------------------------------
Button:
if GameEnd
	return

Gui, Submit, NoHide
RegExMatch(A_GuiControl, "Button(\d+)_(\d+)", m)
if (m1 <> row)
{
	thisPeg := Grid[m1, m2]
	for i, v in pegs
		if (v=thisPeg)
			GuiControl,, Radio%i%, 1
	GuiControl,, % "Button" row "_" m2, % thisPeg
	Grid[row,m2] := thisPeg
}
else
{
	loop, % pegs.count()
		if Radio%A_Index%
			GuiControl,, % A_GuiControl , % grid[m1, m2] := pegs[A_Index]
}
return
;-----------------------------------------------------------------------
Submit:
if (grid[row].count()<4) || GameEnd
	return

Gui, submit, NoHide
Ans := [], FIP := [], inGoal := []
CIP := CNP := 0, KeyPeg := 1

for i, G in Goal
	inGoal[G] := (inGoal[G] ? inGoal[G] : 0) +1		; save inGoal
loop, 4
	Ans[A_Index] := Grid[row, A_Index]			; save Ans
for i, A in Ans
	if (goal[A_Index] = A)
		CIP++, FIP.push(i), inGoal[A]:=inGoal[A] -1	; Correct In Place, inGoal--
for i, v in FIP
	Ans.RemoveAt(v-i+1)					; remove Correct In Place from Answers
for i, A in Ans
	if (inGoal[A] > 0)
		CNP++, inGoal[A] := inGoal[A] -1		; Correct Not in Place
loop % CIP
	GuiControl,, % "KeyPeg" row "_" KeyPeg++, % Chr(82)	; "✔"
loop % CNP
	GuiControl,, % "KeyPeg" row "_" KeyPeg++, % Chr(83)	; "X"

if (CIP=4 || row=maxRows)
{
	loop 4
		GuiControl,, Goal%A_Index%, % Goal[A_Index]
	MsgBox % CIP = 4 ? "You Win" : "You lose"
	GameEnd := true
}
Row++
return
;-----------------------------------------------------------------------
LAlt:: ; peak at solution (for troubleshooting purposes only!)
loop 4
	GuiControl,, Goal%A_Index%, % Goal[A_Index]
While GetKeyState("Lalt", "P")
	continue
loop 4
	GuiControl,, Goal%A_Index%, % "?"
return
;-----------------------------------------------------------------------
ResetMM:
Grid :=[], GameEnd:= false
loop, 4
{
	Random, rnd, 1, % pegs.count()
	goal[A_Index] := pegs[rnd]
	GuiControl,, Goal%A_Index%, ?
}

loop, % maxRows
{
	row := maxRows - A_Index + 1
	loop 4
	{
		col := A_Index
		GuiControl,, % "KeyPeg" row "_" col, % Chr(167)	; "O"
		GuiControl,, % "Button" row "_" col
	}
}
gosub Decode
loop, 8
	GuiControl,, Radio%A_Index%, % pegs[A_Index]
return
;-----------------------------------------------------------------------

BASIC

FreeBASIC

'--- Declaration of global variables ---
Dim As String colors(1 To 4) => {"A", "B", "C", "D"}
Dim Shared As Integer nr, ub', numlet=4, lencod=4
Dim Shared As String*4 master, pz
ub = Ubound(colors)
nr = 0

'--- SUBroutines and FUNCtions ---
Sub Encabezado
    Dim As String dup
    Color 11: Print "Welcome to Mastermind"
    Print "=====================" + Chr(13) + Chr(10) : Color 15
    Print "You will need to guess a random code."
    Print "For each guess, you will receive a hint:"
    Print "X - denotes a correct letter,"
    Print "O - denotes a letter in the original"
    Print "    string but a different position."
    Print "You have 12 attempts."
    Print "Duplicates are not allowed." + Chr(10)
    Print "Good luck!" + Chr(10) + Chr(10) : Color 7    
End Sub 

Sub showresult(test() As String, place1 As Byte, place2 As Byte, place3 As Byte)
    Dim As Integer r, n1, n2, n3
    Print Using "##: "; nr;
    For r = 1 To Ubound(test)
        Print test(r);
    Next R
    Print "  : ";
    For n1 = 1 To place1
        Print "X"; " ";
    Next N1
    For n2 = 1 To place2
        Print "O"; " ";
    Next N2
    For n3 = 1 To place3
        Print "-"; " ";
    Next N3
    Print : Print
End Sub

Sub Inicio
    Dim As Integer mind(ub), rands(ub)
    Dim As Integer n, aleat
    Dim As Boolean repeat = false
    
    For n = 1 To ub
        While true
            aleat = (Rnd * (ub-1)) + 1
            If rands(aleat) <> 1 Then
                mind(n) = aleat
                rands(aleat) = 1
                Exit While
            End If
        Wend
    Next n
    
    For n = 1 To ub
        Mid(master,n,1) = Chr(64 + mind(n))
        pz &= Chr(64 + mind(n))
    Next n
End Sub


'--- Main Program ---
Randomize Timer
Cls
Dim As Integer guesses = 12
Encabezado
Inicio
Color 15: Print pz : Color 7
Do
    Dim As Integer n, p, d, x, posic
    Dim As Integer places(1 To 2), place1, place2, place3
    Dim As String*4 testbegin
    Dim As String test(ub), mastertemp, tmp
    Dim As Boolean flag = True   
    
    For p = 1 To Ubound(places)
        places(p) = 0
    Next p
    nr += 1
    Input "Your guess (ABCD)? " , testbegin
    For d = 1 To Ubound(test)
        test(d) = Mid(testbegin,d,1)
    Next d
    
    For n = 1 To Ubound(test)
        If Ucase(test(n)) <> Mid(master,n,1) Then flag = False
    Next n
    If flag = True Then 
        Color 10: Print !"\nWell done! You guess correctly." : Sleep : Exit Do
    Else
        For x = 1 To Len(master)
            If Ucase(test(x)) = Mid(master,x,1) Then places(1) += 1
        Next x
        mastertemp = master
        For p = 1 To Ubound(test)
            posic = Instr(mastertemp, Ucase(test(p)))
            If posic > 0 Then
                tmp = mastertemp
                mastertemp = Left(tmp,posic-1) + Mid(tmp, posic+1, Len(tmp)-1)
                places(2) += 1
            End If
        Next p
    End If
    place1 = places(1) 
    place2 = places(2) - place1
    place3 = Len(master) - (place1 + place2)
    showresult(test(), place1, place2, place3)
Loop Until nr = guesses
Color 14: Print "The correct combination was: "; pz
Color 7: Print !"\nEnd of game"
Sleep

C++

#include <iostream>
#include <algorithm>
#include <ctime>
#include <string>
#include <vector>

typedef std::vector<char> vecChar;

class master {
public:
    master( size_t code_len, size_t clr_count, size_t guess_count, bool rpt ) {
        std::string color = "ABCDEFGHIJKLMNOPQRST";

        if( code_len < 4 ) code_len = 4; else if( code_len > 10 ) code_len = 10;
        if( !rpt && clr_count < code_len ) clr_count = code_len; 
        if( clr_count < 2 ) clr_count = 2; else if( clr_count > 20 ) clr_count = 20;
        if( guess_count < 7 ) guess_count = 7; else if( guess_count > 20 ) guess_count = 20;
        
        codeLen = code_len; colorsCnt = clr_count; guessCnt = guess_count; repeatClr = rpt;

        for( size_t s = 0; s < colorsCnt; s++ ) {
            colors.append( 1, color.at( s ) );
        }
    }
    void play() {
        bool win = false;
        combo = getCombo();

        while( guessCnt ) {
            showBoard();
            if( checkInput( getInput() ) ) {
                win = true;
                break;
            }
            guessCnt--;
        }
        if( win ) {
            std::cout << "\n\n--------------------------------\n" <<
                "Very well done!\nYou found the code: " << combo <<
                "\n--------------------------------\n\n";
        } else {
            std::cout << "\n\n--------------------------------\n" <<
                "I am sorry, you couldn't make it!\nThe code was: " << combo <<
                "\n--------------------------------\n\n";
        }
    }
private:
    void showBoard() {
        vecChar::iterator y;
        for( int x = 0; x < guesses.size(); x++ ) {
            std::cout << "\n--------------------------------\n";
            std::cout << x + 1 << ": ";
            for( y = guesses[x].begin(); y != guesses[x].end(); y++ ) {
                std::cout << *y << " ";
            }

            std::cout << " :  ";
            for( y = results[x].begin(); y != results[x].end(); y++ ) {
                std::cout << *y << " ";
            }

            int z = codeLen - results[x].size();
            if( z > 0 ) {
                for( int x = 0; x < z; x++ ) std::cout << "- ";
            }
        }
        std::cout << "\n\n";
    }
    std::string getInput() {
        std::string a;
        while( true ) {
            std::cout << "Enter your guess (" << colors << "): ";
            a = ""; std::cin >> a;
            std::transform( a.begin(), a.end(), a.begin(), ::toupper );
            if( a.length() > codeLen ) a.erase( codeLen );
            bool r = true;
            for( std::string::iterator x = a.begin(); x != a.end(); x++ ) {
                if( colors.find( *x ) == std::string::npos ) {
                    r = false;
                    break;
                }
            }
            if( r ) break;
        }
        return a;
    }
    bool checkInput( std::string a ) {
        vecChar g;
        for( std::string::iterator x = a.begin(); x != a.end(); x++ ) {
            g.push_back( *x );
        }
        guesses.push_back( g );
        
        int black = 0, white = 0;
        std::vector<bool> gmatch( codeLen, false );
        std::vector<bool> cmatch( codeLen, false );
 
        for( int i = 0; i < codeLen; i++ ) {
            if( a.at( i ) == combo.at( i ) ) {
                gmatch[i] = true;
                cmatch[i] = true;
                black++;
            }
        }
 
        for( int i = 0; i < codeLen; i++ ) {
            if (gmatch[i]) continue;
            for( int j = 0; j < codeLen; j++ ) {
                if (i == j || cmatch[j]) continue;
                if( a.at( i ) == combo.at( j ) ) {
                    cmatch[j] = true;
                    white++;
                    break;
                }
            }
        }
       
        vecChar r;
        for( int b = 0; b < black; b++ ) r.push_back( 'X' );
        for( int w = 0; w < white; w++ ) r.push_back( 'O' );
        results.push_back( r );

        return ( black == codeLen );
    }
    std::string getCombo() {
        std::string c, clr = colors;
        int l, z;

        for( size_t s = 0; s < codeLen; s++ ) {
            z = rand() % ( int )clr.length();
            c.append( 1, clr[z] );
            if( !repeatClr ) clr.erase( z, 1 );
        }
        return c;
    }

    size_t codeLen, colorsCnt, guessCnt;
    bool repeatClr;
    std::vector<vecChar> guesses, results;
    std::string colors, combo;
};

int main( int argc, char* argv[] ) {
    srand( unsigned( time( 0 ) ) );
    master m( 4, 8, 12, false );
    m.play();
    return 0;
}
Output:
Enter your guess (ABCDEFGH): gbda

--------------------------------
1: A B C D  :  X O O -
--------------------------------
2: A A A E  :  O - - -
--------------------------------
3: E E E E  :  - - - -
--------------------------------
4: B B B C  :  X - - -
--------------------------------
5: D B A F  :  X O O -
--------------------------------
6: G B D A  :  X X X -

Enter your guess (ABCDEFGH): hbda


--------------------------------
Very well done!
You found the code: HBDA
--------------------------------

EasyLang

Run it

# Mastermind:w90
#
col[] = [ 802 990 171 229 950 808 ]
len code[] 4
len guess[] 4
#
subr init_vars
   row = 0
.
proc draw_rate r black white . .
   for j range0 2
      for c range0 2
         move c * 3.5 + 71.5 r * 11.5 + 9.4 - j * 3.5
         if black > 0
            color 000
            circle 1.4
            black -= 1
         elif white > 0
            color 999
            circle 1.4
            white -= 1
         else
            color 310
            circle 0.7
         .
      .
   .
.
proc show_code . .
   color 531
   move 22 92
   rect 46 8
   for i to 4
      move i * 8 + 20 97
      color col[code[i]]
      circle 2
   .
.
proc draw_guess . .
   for c to 4
      move c * 12 + 8 row * 11.5 + 7.5
      color col[guess[c]]
      circle 3.8
   .
.
proc next_row . .
   color 420
   linewidth 11
   move 17 row * 11.5 + 7.5
   line 60 row * 11.5 + 7.5
   draw_guess
   move 73.5 row * 11.5 + 7.5
   color 310
   circle 5.0
   color 753
   move 71.5 row * 11.5 + 5
   textsize 7
   text "✓"
.
proc rate . .
   move 73.5 row * 11.5 + 7.5
   color 531
   circle 5.2
   c[] = code[]
   g[] = guess[]
   for i to 4
      if c[i] = g[i]
         black += 1
         c[i] = -1
         g[i] = -2
      .
   .
   for i to 4
      for j to 4
         if c[i] = g[j]
            white += 1
            c[i] = -1
            g[j] = -2
         .
      .
   .
   draw_rate row black white
   color 531
   linewidth 12
   move 17 row * 11.5 + 7.5
   line 60 row * 11.5 + 7.5
   draw_guess
   row += 1
   if black = 4
      row = 8
   .
   if row = 8
      show_code
      timer 2
   else
      next_row
   .
.
on timer
   row = -2
.
proc new . .
   init_vars
   for i to 4
      code[i] = random 6
   .
   color 531
   move 10 10
   rect 70 80
   linewidth 10
   move 5 95
   line 5 5
   line 85 5
   line 85 95
   line 5 95
   color 310
   linewidth 7
   move 28 96.5
   line 58 96.5
   move 30 95
   color 864
   textsize 4
   text "Mastermind"
   color 310
   linewidth 0.5
   move 10 90
   line 10 4
   move 67 90
   line 67 4
   move 80 90
   line 80 4
   for r range0 8
      for c range0 4
         move c * 12 + 20 r * 11.5 + 7.5
         circle 2
      .
      draw_rate r 0 0
   .
   guess[1] = 1
   guess[2] = 1
   guess[3] = 2
   guess[4] = 2
   next_row
.
proc do_move . .
   c = (mouse_x - 15) div 12
   guess[c + 1] = guess[c + 1] mod 6 + 1
   draw_guess
.
on mouse_down
   if row = -2
      new
   elif mouse_y > row * 11.5 + 0.5 and mouse_y < row * 11.5 + 10.5 and row < 8
      if mouse_x > 15 and mouse_x < 61
         do_move
      elif mouse_x > 67 and mouse_x < 80
         rate
      .
   .
.
new

FutureBasic

This program displays the colours similar to the board game, although it only allows 11 colours, more than that makes it difficult to discern differences.

_window = 1
_Check = 250
_NewGame = 251

_view = 2000

_PrefWnd = 2
begin enum 1
  _NoOfColours
  _Label
  _CodeLgth
  _Label1
  _Guesses
  _Repeats
  _Label2
  _Exit
  _info
end enum

begin enum 1000
  _blue
  _Red
  _Yellow
  _Magenta
  _Orange
  _Green
  _Brown
  _Cyan
  _Purple
  _DarkGray
end enum

_mApplication = 0
begin enum 0
  _iAbout
  _iSeparator
  _PreferencesItem
  _iSeparator1
  _iHide
end enum

_EditMenu = 1

begin enum
  _iUndo
  _iRedo
  _
  _iCut
  _iCopy
  _iPaste
  _iDelete
  _iSelectAll
end enum


begin globals
CFStringRef gColours, gCodeLgth, gGuesses
BOOL gRepeats = NO, gWon = NO
ColorRef gNewColour
int gNextFld = 1, gRestriction = 1
CFMutableArrayRef gArray
CFMutableArrayRef gTargetArray
CFMutableArrayRef gTargetColours
CFMutableArrayRef gGuessArray
int gLine = 1, gLastGuess, gLength
int gColor(12)
CFMutableArrayRef gRestrict
end globals

// Colours 2 - 12
// Code Lgth 4 - 10
// Guesses 7 - 20 total fields 10*20 = 200

gArray = fn MutableArrayWithCapacity(0)
gTargetArray = fn MutableArrayWithCapacity(0)
gGuessArray = fn MutableArrayWithCapacity(0)
gRestrict = fn MutableArrayWithCapacity(0)
gTargetColours = fn MutableArrayWithCapacity(0)

// Master Mind game

void local fn SetBackgroundColor( col as ColorRef )
  TextFieldRef fld = fn ViewWithTag(gNextFld)
  UndoManagerRef um = fn ResponderUndoManager( fld )
  UndoManagerRegisterUndo( um, @fn SetBackgroundColor, fn TextFieldBackgroundColor(fld))
  UndoManagerSetActionName( um, @"Set Background Color" )
  TextFieldSetBackgroundColor( fld, col )
end fn

LOCAL FN Max(Big as int,Little AS int) as int
  int MaxNo
  IF Big > Little THEN MaxNo = Big ELSE MaxNo  = Little
END FN = MaxNo

void local fn SetColor
  for int x = 0 to 11
    gColor(x) = x
  next
end fn

local fn RandomChoice( count as int) as int
  int x,i
  Bool check = NO
  DO
    x = rnd( count + 1 ) - 1
    if gColor(x) > -1
      i = gColor(x )
      if gColor(x) == 0
        gColor(x) = -1
      else
        gColor(x) = -gColor(x)
      end if
      check = YES
    end if
  until check == YES
end fn = i

void local fn Winning
  alert -1,, @"Message", @"You Won This Game", @"OK;Continue", YES
  AlertButtonSetKeyEquivalent( 1, 1, @"\e" )
  alert 1
  gWon = YES
end fn

void local fn SetTarget
  int count =   fn StringIntValue( gColours )
  int x, y
  CFStringRef key
  ColorRef col
  MutableArrayRemoveAllObjects( gTargetArray )
  MutableArrayRemoveAllObjects( gTargetColours )
  
  for x = 0 to count - 1
    if gRepeats == NO
      y = fn RandomChoice( count )
    else
      y = rnd( count + 1 ) - 1
    end if
    key = fn StringWithFormat( @"%d", y)
    col = fn ArrayObjectAtIndex( gArray, y )
    MutableArrayInsertObjectAtIndex( gTargetColours,col, x )
    MutableArrayInsertObjectAtIndex( gTargetArray,key, x )
  next
end fn

void local fn SetFields
  Int x,y,z = 1,xx,yy,zz = 299
  int CodeLgth = fn StringIntValue( gCodeLgth )
  int Guesses = fn StringIntValue( gGuesses )
  CGRect r, lr
  gLastGuess = Guesses
  xx = 20:yy = 40
  r = fn CGRectMake( xx, yy, 25, 25 )
  lr = fn CGRectMake( xx+CodeLgth*25 + 50, yy + 6, 12,12 )
  for x = 1 to Guesses
    for y = 1 to CodeLgth
      textfield z,,@"", r
      ControlSetFontWithName(z,@"Times",12)
      ControlSetAlignment( z, NSTextAlignmentCenter )
      TextFieldSetBackgroundColor( z, fn ColorWhite )
      r = fn CGRectOffset( r, 25, 0)
      textfield z+zz,,@"",lr
      TextFieldSetBackgroundColor( z+zz, fn ColorLightGray )
      z++
      lr = fn CGRectOffset( lr, 12,0)
    next
    lr = fn CGRectOffset( lr, -12*CodeLgth, 25 )
    r = fn CGRectOffset( r,-CodeLgth*25, 25)
  next
end fn

local fn FindColourAtPixel( tag as long ) as ColorRef
End Fn = fn ViewColorAtPoint( tag, fn EventLocationInView( tag ))

local fn ClearTarget
  int x, z = 3000
  int CodeLgth = fn StringIntValue( gCodeLgth )
  
  for x = 0 to CodeLgth-1
    TextFieldSetBackgroundColor( z, fn ColorClear )
    z++
  next
  textlabel 3100, @""
end fn

local fn ShowTarget
  int x, z = 3000
  int CodeLgth = fn StringIntValue( gCodeLgth )
  int Guesses = fn StringIntValue( gGuesses )
  CGRect rr = fn CGRectMake( 20, Guesses*30 + 30, 25,25 )
  
  for x = 0 to CodeLgth-1
    textfield z,,, rr
    TextFieldSetBackgroundColor( z, fn ArrayObjectAtIndex( gTargetColours, x ) )
    rr = fn CGRectOffset( rr, 25, 0 )
    z++
  next
  textlabel 3100, @"Target Array", ( 20, Guesses*30 + 60, 100, 26 )
end fn

void local fn BuildWnd
  ColorRef col
  Int x,z = 1,offset = 200
  CGRect r, rr
  int lgth, wide
  int CodeLgth = fn StringIntValue( gCodeLgth )
  int Guesses = fn StringIntValue( gGuesses )
  int Colour = fn StringIntValue( gColours )
  if Colour <= CodeLgth
    select CodeLgth
      case 4,5,6,7
        Colour += 3
      case 8,9,10
        Colour = 12
    end select
  end if
  if Guesses < 9 && Colour > 9 then offset += (Colour-Guesses) * 25
  CFArrayRef array = @[fn ColorBlue,fn ColorRed,fn ColorYellow,fn ColorMagenta,fn ColorOrange,fn ColorGreen,fn ColorBrown,fn ColorCyan,fn ColorPurple,fn ColorDarkGray,fn ColorSystemPink,fn ColorSystemTeal]
  MutableArrayAddObjectsFromArray( gArray, array )
  wide =  CodeLgth*37 + 180
  lgth = fn Max(Guesses*27 + offset, Colour*30 + 50 )
  gLength = lgth
  window _window, @"Master Mind", ( 210,310,wide, lgth )
  ViewSetFlipped(_windowContentViewTag, YES)
  fn SetFields
  subclass view _view, ( wide - 65, 20,50, lgth - 60)
  ViewSetFlipped( _view, YES )
  rr = fn CGRectMake( wide - 65, 20,50, lgth - 60)
  rect rr,,8
  r = fn CGRectMake( 15, 15, 25,25)
  z = 1000
  for x = 0 to Colour - 1
    col = fn ArrayObjectAtIndex( array, x)
    subclass view  z, r
    ViewSetWantsLayer( z, YES )
    CALayerSetBackgroundColor( fn ViewLayer(z), col )
    ViewInitTrackingArea( z )
    ViewAddSubView( _view, z )
    r = fn CGRectOffset( r,0,30 )
    z++
  next
  
  button _Check, , , @"Check", ( 30, lgth - 65, 100, 26)
  button _NewGame, , ,@"New Game", (150, lgth - 65, 100, 26 )
  
end fn

void local fn Capture( wnd as long )
  int y, z
  CFStringRef txt = @""
  
  select Wnd
    case _PrefWnd
      gColours = fn PopUpButtonTitleOfSelectedItem(_NoOfColours)
      gCodeLgth = fn PopUpButtonTitleOfSelectedItem(_CodeLgth)
      gGuesses = fn PopUpButtonTitleOfSelectedItem(_Guesses)
      if fn ButtonState( _Repeats ) == NSControlStateValueOn then gRepeats = YES else gRepeats = NO
      fn SetColor
    case _window
      //if fn ButtonState( _Repeats ) == NSControlStateValueOn then gRepeats = YES else gRepeats = NO
      z = fn StringIntValue( gCodeLgth )
      y = gLine*z - z + 1
      MutableArrayRemoveAllObjects( gGuessArray )
      for int x = y to (y + z - 1)
        txt = fn ControlStringValue( x)
        MutableArrayAddObject(gGuessArray, txt )
      next
      gLine++
      if gLine > gLastGuess
        fn ShowTarget
        alert -1,, @"Message", @"You Fail to win this Game", @"OK;Continue", YES
        AlertButtonSetKeyEquivalent( 1, 1, @"\e" )
        alert 1
        gWon = NO
      end if
  end select
end fn

void local fn Compare
  int x,y,count = fn StringIntValue( gCodeLgth )
  CFTypeRef target,guess,target1
  bool won = YES
  
  fn Capture( _window )
  gRestriction = 1
  //Check for location and colour
  for x = 0 to count - 1
    target = fn ArrayObjectAtIndex( gTargetArray, x)
    guess = fn ArrayObjectAtIndex( gGuessArray, x)
    if target == guess
      TextFieldSetBackgroundColor( (gLine-2)*count + 300 + x, fn ColorBlack )
    else
      for y = 0 to count - 1
        won = NO
        target1 = fn ArrayObjectAtIndex( gTargetArray, y)
        if target1 == guess
          TextFieldSetBackgroundColor( (gLine-2)*count + 300 + x, fn ColorWhite )
        end if
      next
    end if
  next
  ControlSetEnabled( _Check, NO )
  MutableArrayRemoveAllObjects( gRestrict )
  if won == YES then fn Winning
end fn

void local fn NewGame
  fn SetColor
  fn SetFields
  if gWon == NO
    fn ClearTarget
  end if
  fn SetTarget
  gLine = 1
  gNextFld = 1
end fn

void local fn Preferences
  CGRect rr, lr
  window _PrefWnd, @"Preferences", ( 0,0,250,350)
  
  rr = fn CGRectMake( 20,220,160,26)
  lr = fn CGRectMake( 20,200, 60, 26 )
  textlabel _label, @"No Of Colours", rr
  popupbutton _NoOfColours,,19, @"2;3;4;5;6;7;8;9;10;11;12", lr
  rr = fn CGRectOffset( rr, 0, -50)
  lr = fn CGRectOffset( lr, 0, -50)
  textlabel _label1, @"No Of Items", rr
  popupbutton _CodeLgth,,7,@"4;5;6;7;8;9;10", lr
  rr = fn CGRectOffset( rr, 0, -50)
  lr = fn CGRectOffset( lr, 0, -50)
  textlabel _label2, @"No Of Guesses", rr
  popupbutton _Guesses,,14,@"4;5;6;7;8;9;10;11;12;13;14;15;16;17;18;19;20", lr
  rr = fn CGRectMake( 100,150,100,26)
  button _Exit,,,@"Begin Game", rr
  checkbox _Repeats,,,@"Repeats Allowed", ( 20, 70 , 160, 26 )
  rr = fn CGRectMake( 10,250, 230, 100)
  textfield _info,,@"Move mouse over coloured square to choose\nThen move away from window\nRepeat for all fields\nThen click Check",rr
  gNextFld = 1
  gRestriction = 1
  UserDefaultsRestoreWindowViewValues( _PrefWnd, NULL )
end fn

void Local Fn BuildMenu  //build menu & get handle
  menu _mApplication, _iAbout
  menu _mApplication, _iSeparator
  menu _mApplication, _PreferencesItem,, @"Settings…", @","
  menu _mApplication, _iSeparator1
  menu _mApplication, _iHide,, @"Hide Master Mind", @"h"
  MenuItemSetAction( _mApplication, _iHide, @"hide:")
  
  EditMenu _EditMenu
  /*
    menu _EditMenu,_iUndo,YES
    MenuItemSetActionCallBack( _EditMenu, _iUndo, @fn SetBackGroundColor, NULL )
    menu _EditMenu,_iRedo
    
    menu _EditMenu,_iCut
    menu _EditMenu,_iCopy
    menu _EditMenu,_iPaste
    menu _EditMenu,_iDelete
    menu _EditMenu,_iSelectAll
	  */
end fn

void local fn doMenu(act as long, ref as long )
  select act
    case _mApplication
      select ref
        case _PreferencesItem
          windowClose( _window)
          fn Preferences
        case else
      end select
    case _EditMenu
      /*
            select ref
            case _iUndo
            gNextFld--
            case _iRedo
            gNextFld++
            case _iCut
            case _iCopy
            case _iPaste
            case _iDelete
            case _iSelectAll
            end select
			      */
  end select
end fn

void local fn doDialog( act as long, ref as long, wnd as long)
  select Wnd
    case _window
      select act
        case _BtnClick
          select ref
            case _Check : fn Compare
            case _NewGame : fn NewGame
              
          end select
        case _viewMouseEntered,_viewMouseDown
          select ref
            if gRepeats == NO && fn ArrayDoesContain( gRestrict, (ObjectRef)fn StringWithFormat( @"%d", ref )) == YES
            else
              if gRestriction < fn StringIntValue( gCodeLgth) + 1
                gNewColour = fn FindColourAtPixel( ref )
                ControlSetStringValue( gNextFld, fn StringWithFormat(@"%d",ref-1000))
                fn SetBackgroundColor( gNewColour )
                if gRepeats == NO
                  MutableArrayAddObject( gRestrict,fn StringWithFormat( @"%d", ref ))
                end if
                gNextFld++
                gRestriction++
              else
                ControlSetEnabled( _Check, YES )
              end if
            end if
          end select
      end select
    case _PrefWnd
      select act
        case _btnClick
          select ref
            case _NoOfColours
              gColours = fn PopUpButtonTitleOfSelectedItem(ref)
            case _CodeLgth
              gCodeLgth = fn PopUpButtonTitleOfSelectedItem(ref)
            case _Guesses
              gGuesses = fn PopUpButtonTitleOfSelectedItem(ref)
            Case _Repeats
              if fn ButtonState( _Repeats ) == NSControlStateValueOn then gRepeats = YES else gRepeats = NO
            case _Exit
              UserDefaultsStoreWindowViewValues( wnd, NULL )
              fn Capture (wnd )
              WindowClose( wnd)
              fn BuildWnd
              fn SetTarget
          end select
      end select
  end select
end fn


fn Preferences
fn BuildMenu


on Dialog fn doDialog
on Menu fn doMenu

HandleEvents
Output:

 

Go

package main

import (
	"errors"
	"flag"
	"fmt"
	"log"
	"math/rand"
	"strings"
	"time"
)

func main() {
	log.SetPrefix("mastermind: ")
	log.SetFlags(0)
	colours := flag.Int("colours", 6, "number of colours to use (2-20)")
	flag.IntVar(colours, "colors", 6, "alias for colours")
	holes := flag.Int("holes", 4, "number of holes (the code length, 4-10)")
	guesses := flag.Int("guesses", 12, "number of guesses allowed (7-20)")
	unique := flag.Bool("unique", false, "disallow duplicate colours in the code")
	flag.Parse()

	rand.Seed(time.Now().UnixNano())
	m, err := NewMastermind(*colours, *holes, *guesses, *unique)
	if err != nil {
		log.Fatal(err)
	}
	err = m.Play()
	if err != nil {
		log.Fatal(err)
	}
}

type mastermind struct {
	colours int
	holes   int
	guesses int
	unique  bool

	code   string
	past   []string // history of guesses
	scores []string // history of scores
}

func NewMastermind(colours, holes, guesses int, unique bool) (*mastermind, error) {
	if colours < 2 || colours > 20 {
		return nil, errors.New("colours must be between 2 and 20 inclusive")
	}
	if holes < 4 || holes > 10 {
		return nil, errors.New("holes must be between 4 and 10 inclusive")
	}
	if guesses < 7 || guesses > 20 {
		return nil, errors.New("guesses must be between 7 and 20 inclusive")
	}
	if unique && holes > colours {
		return nil, errors.New("holes must be > colours when using unique")
	}

	return &mastermind{
		colours: colours,
		holes:   holes,
		guesses: guesses,
		unique:  unique,
		past:    make([]string, 0, guesses),
		scores:  make([]string, 0, guesses),
	}, nil
}

func (m *mastermind) Play() error {
	m.generateCode()
	fmt.Printf("A set of %s has been selected as the code.\n", m.describeCode(m.unique))
	fmt.Printf("You have %d guesses.\n", m.guesses)
	for len(m.past) < m.guesses {
		guess, err := m.inputGuess()
		if err != nil {
			return err
		}
		fmt.Println()
		m.past = append(m.past, guess)
		str, won := m.scoreString(m.score(guess))
		if won {
			plural := "es"
			if len(m.past) == 1 {
				plural = ""
			}
			fmt.Printf("You found the code in %d guess%s.\n", len(m.past), plural)
			return nil
		}
		m.scores = append(m.scores, str)
		m.printHistory()
		fmt.Println()
	}
	fmt.Printf("You are out of guesses. The code was %s.\n", m.code)
	return nil
}

const charset = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
const blacks = "XXXXXXXXXX"
const whites = "OOOOOOOOOO"
const nones = "----------"

func (m *mastermind) describeCode(unique bool) string {
	ustr := ""
	if unique {
		ustr = " unique"
	}
	return fmt.Sprintf("%d%s letters (from 'A' to %q)",
		m.holes, ustr, charset[m.colours-1],
	)
}

func (m *mastermind) printHistory() {
	for i, g := range m.past {
		fmt.Printf("-----%s---%[1]s--\n", nones[:m.holes])
		fmt.Printf("%2d:  %s : %s\n", i+1, g, m.scores[i])
	}
}

func (m *mastermind) generateCode() {
	code := make([]byte, m.holes)
	if m.unique {
		p := rand.Perm(m.colours)
		for i := range code {
			code[i] = charset[p[i]]
		}
	} else {
		for i := range code {
			code[i] = charset[rand.Intn(m.colours)]
		}
	}
	m.code = string(code)
	//log.Printf("code is %q", m.code)
}

func (m *mastermind) inputGuess() (string, error) {
	var input string
	for {
		fmt.Printf("Enter guess #%d: ", len(m.past)+1)
		if _, err := fmt.Scanln(&input); err != nil {
			return "", err
		}
		input = strings.ToUpper(strings.TrimSpace(input))
		if m.validGuess(input) {
			return input, nil
		}
		fmt.Printf("A guess must consist of %s.\n", m.describeCode(false))
	}
}

func (m *mastermind) validGuess(input string) bool {
	if len(input) != m.holes {
		return false
	}
	for i := 0; i < len(input); i++ {
		c := input[i]
		if c < 'A' || c > charset[m.colours-1] {
			return false
		}
	}
	return true
}

func (m *mastermind) score(guess string) (black, white int) {
	scored := make([]bool, m.holes)
	for i := 0; i < len(guess); i++ {
		if guess[i] == m.code[i] {
			black++
			scored[i] = true
		}
	}
	for i := 0; i < len(guess); i++ {
		if guess[i] == m.code[i] {
			continue
		}
		for j := 0; j < len(m.code); j++ {
			if i != j && !scored[j] && guess[i] == m.code[j] {
				white++
				scored[j] = true
			}
		}
	}
	return
}

func (m *mastermind) scoreString(black, white int) (string, bool) {
	none := m.holes - black - white
	return blacks[:black] + whites[:white] + nones[:none], black == m.holes
}
Output (using Knuth's five-guess algorithm):
A set of 4 letters (from 'A' to 'F') has been selected as the code.
You have 12 guesses.
[... output of first guesses omitted ...]
Enter guess #4: FEDE

------------------
 1:  AABB : ----
------------------
 2:  FFED : XOOO
------------------
 3:  DFDF : XO--
------------------
 4:  FEDE : XOOO

Enter guess #5: EFFE

You found the code in 5 guesses.

Java

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;
import java.util.concurrent.ThreadLocalRandom;

public final class MastermindTask {

	public static void main(String[] aArgs) {
	    Mastermind mastermind = new Mastermind(4, 8, 12, false);
	    mastermind.play();
	}
	
	private static final class Mastermind {
		
	    public Mastermind(int aCodeLength, int aLetterCount, int aGuessCount, boolean aRepeatLetters) {
	        if ( aCodeLength < 4 ) {
	        	aCodeLength = 4; 
	        } else if ( aCodeLength > 10 ) {
	        	aCodeLength = 10;
	        }
	        
	        if ( aLetterCount < 2 ) {
	        	aLetterCount = 2;
	        } else if ( aLetterCount > 20 ) {
	        	aLetterCount = 20;
	        }
	        
	        if ( aGuessCount < 7 ) {
	        	aGuessCount = 7; 
	        } else if ( aGuessCount > 20 ) {
	        	aGuessCount = 20;
	        }	
	        
	        if ( ! aRepeatLetters && aLetterCount < aCodeLength ) {
	        	aLetterCount = aCodeLength; 
	        }                
	        
	        codeLength = aCodeLength;
	        letterCount = aLetterCount;
	        guessCount = aGuessCount;
	        repeatLetters = aRepeatLetters;

	        String validLetters = "ABCDEFGHIJKLMNOPQRST";
	        letters = "";
	        for ( int i = 0; i < letterCount; i++ ) {
	            letters += validLetters.charAt(i);
	        }
	    }
	    
	    public void play() {
	        boolean playerWin = false;
	        goal = createGoal();

	        while ( guessCount > 0 && ! playerWin ) {
	            showBoard();
	            if ( checkUserInput(obtainUserGuess()) ) {
	                playerWin = true;
	                reader.close();
	            }
	            guessCount--;
	        }
	        
	        if ( playerWin ) {
	            System.out.println(newLine + newLine + "--------------------------------" + newLine + 
	                "Very well done! " + newLine + "You found the code: " + goal +
	                newLine + "--------------------------------" + newLine + newLine);
	        } else {
	            System.out.println(newLine + newLine + "--------------------------------" + newLine +
	                "I'm sorry, you couldn't make it! " + newLine + "The code was: " + goal +
	                newLine + "--------------------------------" + newLine + newLine);
	        }
	    }
	    
	    private void showBoard() {
	        for ( int i = 0; i < guesses.size(); i++ ) {
	            System.out.print(newLine + "--------------------------------" + newLine);
	            System.out.print(( i + 1 ) + ": ");
	            for ( char ch : guesses.get(i) ) {
	                System.out.print(ch + " ");
	            }

	            System.out.print(" :  ");
	            for ( char ch : results.get(i) ) {
	                System.out.print(ch + " ");
	            }

	            final int errorCount = codeLength - results.get(i).size();
                for ( int j = 0; j < errorCount; j++ ) {
                	System.out.print("- ");
                }
	        }
	        System.out.print(newLine + newLine);
	    }	    
	    
	    private String obtainUserGuess() {
	        String result = "";
	        do {
	        	System.out.print("Enter your guess (" + letters + "): ");	            
	        	result = reader.nextLine().toUpperCase();
	        	if ( result.length() != codeLength ) {
	        		System.out.println("Please try again, your guess should have " + codeLength + " letters");
	        	}	        	
	        } while ( result.length() != codeLength );	
	        return result;
	    }
	    
	    private boolean checkUserInput(String aUserInput) {
	        List<Character> userInputCharacters = new ArrayList<Character>();
	        for ( char ch : aUserInput.toCharArray() ) {
	            userInputCharacters.add(ch);
	        }
	        guesses.add(userInputCharacters);
	        
	        int xCount = 0;
	        int oCount = 0;
	        List<Boolean> fullMatches = new ArrayList<Boolean>(Collections.nCopies(codeLength, false));
	        List<Boolean> partialMatches = new ArrayList<Boolean>(Collections.nCopies(codeLength, false));
	        
	        for ( int i = 0; i < codeLength; i++ ) {
	            if ( aUserInput.charAt(i) == goal.charAt(i) ) {
	                fullMatches.set(i, true);
	                partialMatches.set(i, true);
	                xCount++;
	            }
	        }
	 
	        for ( int i = 0; i < codeLength; i++ ) {
	            if ( fullMatches.get(i) ) {
	            	continue;
	            }
	            for ( int j = 0; j < codeLength; j++ ) {
	                if ( i == j || partialMatches.get(j) ) {
	                	continue;
	                }
	                if ( aUserInput.charAt(i) == goal.charAt(j) ) {
	                    partialMatches.set(j, true);
	                    oCount++;
	                    break;
	                }
	            }
	        }
	       
	        List<Character> nextResult = new ArrayList<Character>();
	        for ( int i = 0; i < xCount; i++ ) {
	        	nextResult.add('X');
	        }
	        for ( int i = 0; i < oCount; i++ ) {
	        	nextResult.add('O');
	        }
	        results.add(nextResult);

	        return xCount == codeLength;
	    }
	    
	    private String createGoal() {
	        String result = "";
	        String lettersCopy = letters;

	        for ( int i = 0; i < codeLength; i++ ) {
	            final int index = random.nextInt(lettersCopy.length());
	            result += lettersCopy.charAt(index);
	            if ( ! repeatLetters ) {
	            	lettersCopy = lettersCopy.substring(0, index) + lettersCopy.substring(index + 1);
	            }
	        }
	        return result;
	    }
	    
	    private int codeLength, letterCount, guessCount;
	    private String letters, goal;
	    private boolean repeatLetters;
	    private Scanner reader = new Scanner(System.in);
	    private List<List<Character>> guesses = new ArrayList<List<Character>>();
	    private List<List<Character>> results = new ArrayList<List<Character>>(); 	    
	    
	    private final ThreadLocalRandom random = ThreadLocalRandom.current();
	    private final String newLine = System.lineSeparator();
	    
	}

}
Output:
Enter your guess (ABCDEFGH): abcd

--------------------------------
1: A B C D  :  X O O - 

Enter your guess (ABCDEFGH): bcde

--------------------------------
1: A B C D  :  X O O - 
--------------------------------
2: B C D E  :  O O O - 

Enter your guess (ABCDEFGH): fbcd

--------------------------------
1: A B C D  :  X O O - 
--------------------------------
2: B C D E  :  O O O - 
--------------------------------
3: F B C D  :  X O O O 

Enter your guess (ABCDEFGH): fbdc

--------------------------------
1: A B C D  :  X O O - 
--------------------------------
2: B C D E  :  O O O - 
--------------------------------
3: F B C D  :  X O O O 
--------------------------------
4: F B D C  :  X X O O 

Enter your guess (ABCDEFGH): 

// continues ...

JavaScript

You can try it here.

class Mastermind {
  constructor() {
    this.colorsCnt;
    this.rptColors;
    this.codeLen;
    this.guessCnt;
    this.guesses;
    this.code;
    this.selected;
    this.game_over;
    this.clear = (el) => {
      while (el.hasChildNodes()) {
        el.removeChild(el.firstChild);
      }
    };
    this.colors = ["🤡", "👹", "👺", "👻", "👽", "👾", "🤖", "🐵", "🐭",
      "🐸", "🎃", "🤠", "☠️", "🦄", "🦇", "🛸", "🎅", "👿", "🐲", "🦋"
    ];
  }

  newGame() {
    this.selected = null;
    this.guessCnt = parseInt(document.getElementById("gssCnt").value);
    this.colorsCnt = parseInt(document.getElementById("clrCnt").value);
    this.codeLen = parseInt(document.getElementById("codeLen").value);
    if (this.codeLen > this.colorsCnt) {
      document.getElementById("rptClr").selectedIndex = 1;
    }
    this.rptColors = document.getElementById("rptClr").value === "yes";
    this.guesses = 0;
    this.game_over = false;
    const go = document.getElementById("gameover");
    go.innerText = "";
    go.style.visibility = "hidden";
    this.clear(document.getElementById("code"));
    this.buildPalette();
    this.buildPlayField();
  }

  buildPalette() {
    const pal = document.getElementById("palette"),
      z = this.colorsCnt / 5,
      h = Math.floor(z) != z ? Math.floor(z) + 1 : z;
    this.clear(pal);
    pal.style.height = `${44 * h + 3 * h}px`;
    const clrs = [];
    for (let c = 0; c < this.colorsCnt; c++) {
      clrs.push(c);
      const b = document.createElement("div");
      b.className = "bucket";
      b.clr = c;
      b.innerText = this.colors[c];
      b.addEventListener("click", () => {
        this.palClick(b);
      });
      pal.appendChild(b);
    }
    this.code = [];
    while (this.code.length < this.codeLen) {
      const r = Math.floor(Math.random() * clrs.length);
      this.code.push(clrs[r]);
      if (!this.rptColors) {
        clrs.splice(r, 1);
      }
    }
  }

  buildPlayField() {
    const brd = document.getElementById("board");
    this.clear(brd);
    const w = 49 * this.codeLen + 7 * this.codeLen + 5;
    brd.active = 0;
    brd.style.width = `${w}px`;
    document.querySelector(".column").style.width = `${w + 20}px`;
    this.addGuessLine(brd);
  }

  addGuessLine(brd) {
    const z = document.createElement("div");
    z.style.clear = "both";
    brd.appendChild(z);
    brd.active += 10;
    for (let c = 0; c < this.codeLen; c++) {
      const d = document.createElement("div");
      d.className = "bucket";
      d.id = `brd${brd.active+ c}`;
      d.clr = -1;
      d.addEventListener("click", () => {
        this.playClick(d);
      })
      brd.appendChild(d);
    }
  }

  palClick(bucket) {
    if (this.game_over) return;
    if (null === this.selected) {
      bucket.classList.add("selected");
      this.selected = bucket;
      return;
    }
    if (this.selected !== bucket) {
      this.selected.classList.remove("selected");
      bucket.classList.add("selected");
      this.selected = bucket;
      return;
    }
    this.selected.classList.remove("selected");
    this.selected = null;
  }

  vibrate() {
    const brd = document.getElementById("board");
    let timerCnt = 0;
    const exp = setInterval(() => {
      if ((timerCnt++) > 60) {
        clearInterval(exp);
        brd.style.top = "0px";
        brd.style.left = "0px";
      }
      let x = Math.random() * 4,
        y = Math.random() * 4;
      if (Math.random() < .5) x = -x;
      if (Math.random() < .5) y = -y;
      brd.style.top = y + "px";
      brd.style.left = x + "px";
    }, 10);
  }

  playClick(bucket) {
    if (this.game_over) return;
    if (this.selected) {
      bucket.innerText = this.selected.innerText;
      bucket.clr = this.selected.clr;
    } else {
      this.vibrate();
    }
  }

  check() {
    if (this.game_over) return;
    let code = [];
    const brd = document.getElementById("board");
    for (let b = 0; b < this.codeLen; b++) {
      const h = document.getElementById(`brd${brd.active + b}`).clr;
      if (h < 0) {
        this.vibrate();
        return;
      }
      code.push(h);
    }
    this.guesses++;
    if (this.compareCode(code)) {
      this.gameOver(true);
      return;
    }
    if (this.guesses >= this.guessCnt) {
      this.gameOver(false);
      return;
    }
    this.addGuessLine(brd);
  }

  compareCode(code) {
    let black = 0,
      white = 0,
      b_match = new Array(this.codeLen).fill(false),
      w_match = new Array(this.codeLen).fill(false);
    for (let i = 0; i < this.codeLen; i++) {
      if (code[i] === this.code[i]) {
        b_match[i] = true;
        w_match[i] = true;
        black++;
      }
    }
    for (let i = 0; i < this.codeLen; i++) {
      if (b_match[i]) continue;
      for (let j = 0; j < this.codeLen; j++) {
        if (i == j || w_match[j]) continue;
        if (code[i] === this.code[j]) {
          w_match[j] = true;
          white++;
          break;
        }
      }
    }
    const brd = document.getElementById("board");
    let d;
    for (let i = 0; i < black; i++) {
      d = document.createElement("div");
      d.className = "pin";
      d.style.backgroundColor = "#a00";
      brd.appendChild(d);
    }
    for (let i = 0; i < white; i++) {
      d = document.createElement("div");
      d.className = "pin";
      d.style.backgroundColor = "#eee";
      brd.appendChild(d);
    }
    return (black == this.codeLen);
  }

  gameOver(win) {
    if (this.game_over) return;
    this.game_over = true;
    const cd = document.getElementById("code");
    for (let c = 0; c < this.codeLen; c++) {
      const d = document.createElement("div");
      d.className = "bucket";
      d.innerText = this.colors[this.code[c]];
      cd.appendChild(d);
    }
    const go = document.getElementById("gameover");
    go.style.visibility = "visible";
    go.innerText = win ? "GREAT!" : "YOU FAILED!";
    const i = setInterval(() => {
      go.style.visibility = "hidden";
      clearInterval(i);
    }, 3000);
  }
}
const mm = new Mastermind();
document.getElementById("newGame").addEventListener("click", () => {
  mm.newGame()
});
document.getElementById("giveUp").addEventListener("click", () => {
  mm.gameOver();
});
document.getElementById("check").addEventListener("click", () => {
  mm.check()
});

To test you'll need a HTML file

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <link rel="stylesheet" href="./css/style.css" type="text/css">
  <title>Mastermind</title>
</head>
<body>
  <div id="gameover"></div>
  <div class="column">
    <div id="board" style="position: relative"></div>
    <div style="clear: both"> </div>
    <button id="check" style="margin-top:20px">Check!</button>
    <button id="giveUp">Give up!</button>
    <div id="code" style="margin-top: 40px"></div>
  </div>
  <div class="columnS">
    <div id="ctrls">
      <label for="clrCnt">Colors count:</label>
      <input type="number" id="clrCnt" max="20" min="2" value="6"></input>
      <br />
      <label for="codeLen">Code length:</label>
      <input type="number" id="codeLen" max="10" min="4" value="4"></input>
      <br />
      <label for="gssCnt">Guesses count:</label>
      <input type="number" id="gssCnt" max="20" min="7" value="12"></input>
      <br />
      <label for="rptClr">Repeat colors:</label>
      <select id="rptClr">
        <option value="no">No</option>
        <option value="yes">Yes</option>
      </select>
      <button id="newGame" style="width: 100%">New game</button>
    </div>
    <div id="palette"></div>
  </div>
  <script src="./src/index.js" type="module"></script>
</body>
</html>

And a CSS file

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  user-select: none;
}
body {
  background-color: #222;
  text-align: left
}
button {
  width: 101px;
  height: 26px;
  background-color: #444;
  color: #ddd;
  border: 1px solid #333;
  border-radius: 4px;
}
input,
select {
  float: right;
  width: 60px;
  height: 24px;
  margin-top: 6px;
  font-size: 20px;
}
#palette {
  margin-top: 40px;
  width: 233px;
  border-radius: 5px;
  border: 1px solid #fff;
}
#ctrls {
  border-radius: 5px;
  border: 1px solid #fff;
  padding: 10px;
  font-size: 20px;
  width: 233px;
  line-height: 36px;
  color: #fff;
}
#gameover {
  position: absolute;
  top: 90px;
  left: 0;
  font-size: 100px;
  text-align: center;
  color: rgb(248, 143, 4);
  background: rgba(34, 34, 34, .8);
  padding: 10px;
  z-index: 999;
}
.column,
.columnS {
  float: left;
  width: 249px;
  margin: 30px;
}
.columnS {
  width: 300px;
  margin-left: 0;
}
.bucket {
  float: left;
  width: 42px;
  height: 42px;
  line-height: 40px;
  font-size: 26px;
  border: 2px solid #fff;
  border-radius: 3px;
  margin: 2px;
  cursor: pointer;
}
.selected {
  border: 2px solid #d00;
}
.pin {
  float: left;
  width: 14px;
  height: 14px;
  border-radius: 50%;
  margin: 2px;
}

Julia

GUI version, uses the Gtk toolkit.

using Gtk, Colors, Cairo, Graphics

struct Guess
    code::Vector{Color}
    guess::Vector{Color}
    hint::Vector{Color}
end

function Guess(code, guess)
    len = length(code)
    hints = fill(colorant"gray", len) # gray default
    for (i, g) in enumerate(guess), (j, c) in enumerate(code)
        if g == c
            if i == j
                hints[i] = colorant"black"
            elseif hints[i] != colorant"black"
                hints[i] = colorant"white"
            end
        end
    end
    g = Guess([c for c in code], [c for c in guess], [c for c in hints])
end

tovec(guess) = [x for x in [guess.code; guess.guess; guess.hint]]

function mastermindapp()
    allu(s) = length(unique(s)) == length(s)
    ccode(c, n, rok) = while true a = rand(c, n); if rok || allu(a) return a end end

    numcolors, codelength, maxguesses, allowrep, gameover = 10, 4, 10, false, false
    colors = distinguishable_colors(numcolors)
    code = ccode(colors, numcolors, allowrep)
    guesshistory = Vector{Guess}()
    
    win = GtkWindow("Mastermind Game", 900, 750) |> (GtkFrame() |> (box = GtkBox(:v)))  
    settingsbox = GtkBox(:h)
    playtoolbar = GtkToolbar()

    setcolors = GtkScale(false, 4:20)
    set_gtk_property!(setcolors, :hexpand, true)
    adj = GtkAdjustment(setcolors)
    set_gtk_property!(adj, :value, 10)
    clabel = GtkLabel("Number of Colors")

    setcodelength = GtkScale(false, 4:10)
    set_gtk_property!(setcodelength, :hexpand, true)
    adj = GtkAdjustment(setcodelength)
    set_gtk_property!(adj, :value, 4)
    slabel = GtkLabel("Code Length")

    setnumguesses = GtkScale(false, 4:40)
    set_gtk_property!(setnumguesses, :hexpand, true)
    adj = GtkAdjustment(setnumguesses)
    set_gtk_property!(adj, :value, 10)
    nlabel = GtkLabel("Max Guesses")

    allowrepeatcolor = GtkScale(false, 0:1)
    set_gtk_property!(allowrepeatcolor, :hexpand, true)
    rlabel = GtkLabel("Allow Repeated Colors (0 = No)")

    newgame = GtkToolButton("New Game")
    set_gtk_property!(newgame, :label, "New Game")
    set_gtk_property!(newgame, :is_important, true)

    tryguess = GtkToolButton("Submit Current Guess")
    set_gtk_property!(tryguess, :label, "Submit Current Guess")
    set_gtk_property!(tryguess, :is_important, true)

    eraselast = GtkToolButton("Erase Last (Unsubmitted) Pick")
    set_gtk_property!(eraselast, :label, "Erase Last (Unsubmitted) Pick")
    set_gtk_property!(eraselast, :is_important, true)

    map(w->push!(settingsbox, w),[clabel, setcolors, slabel, setcodelength,
        nlabel, setnumguesses, rlabel, allowrepeatcolor])
    map(w->push!(playtoolbar, w),[newgame, tryguess, eraselast])
    
    scrwin = GtkScrolledWindow()
    can = GtkCanvas()
    set_gtk_property!(can, :expand, true)
    map(w -> push!(box, w),[settingsbox, playtoolbar, scrwin])
    push!(scrwin, can)

    currentguess = RGB[]
    guessesused = 0
    colorpositions = Point[]
    
    function newgame!(w)
        empty!(guesshistory)
        
        numcolors = Int(GAccessor.value(setcolors))
        codelength = Int(GAccessor.value(setcodelength))
        maxguesses = Int(GAccessor.value(setnumguesses))
        allowrep = Int(GAccessor.value(allowrepeatcolor))
        
        colors = distinguishable_colors(numcolors)
        code = ccode(colors, codelength, allowrep == 1)
        empty!(currentguess)
        currentneeded = codelength
        guessesused = 0
        gameover = false
        draw(can)
    end
    signal_connect(newgame!, newgame, :clicked)
       
    function saywon!()
        warn_dialog("You have WON the game!", win)
        gameover = true
    end

    function outofguesses!()
        warn_dialog("You have Run out of moves! Game over.", win)
        gameover = true    
    end
    
    can.mouse.button1press = @guarded (widget, event) -> begin
        if !gameover && (i = findfirst(p -> 
            sqrt((p.x - event.x)^2 + (p.y - event.y)^2) < 20,
                colorpositions)) != nothing
            if length(currentguess) < codelength
                if allowrep == 0 && !allu(currentguess)
                    warn_dialog("Please erase the duplicate color.", win)
                else
                    push!(currentguess, colors[i])
                    draw(can)
                end
            else
                warn_dialog("You need to submit this guess if ready.", win)
            end
        end
    end
    
    @guarded draw(can) do widget
        ctx = Gtk.getgc(can)
        select_font_face(ctx, "Courier", Cairo.FONT_SLANT_NORMAL, Cairo.FONT_WEIGHT_BOLD)
        fontpointsize = 12
        set_font_size(ctx, fontpointsize)
        workcolor = colorant"black"
        set_source(ctx, workcolor)
        move_to(ctx, 0, fontpointsize)
        show_text(ctx, "Color options: " * "-"^70)
        stroke(ctx)
        empty!(colorpositions)
        for i in 1:numcolors
            set_source(ctx, colors[i])
            circle(ctx, i * 40, 40, 20)
            push!(colorpositions, Point(i * 40, 40))
            fill(ctx)
        end
        set_gtk_property!(can, :expand, false) # kludge for good text overwriting
        move_to(ctx, 0, 80)
        set_source(ctx, workcolor)
        show_text(ctx, string(maxguesses - guessesused, pad = 2) * " moves remaining.")
        stroke(ctx)
        set_gtk_property!(can, :expand, true)
        for i in 1:codelength
            set_source(ctx, i > length(currentguess) ? colorant"lightgray" : currentguess[i])
            circle(ctx, i * 40, 110, 20)
            fill(ctx)
        end
        if length(guesshistory) > 0
            move_to(ctx, 0, 155)
            set_source(ctx, workcolor)
            show_text(ctx, "Past Guesses: " * "-"^70)
            for (i, g) in enumerate(guesshistory), (j, c) in enumerate(tovec(g)[codelength+1:end])
                x = j * 40 + (j > codelength ? 20 : 0)
                y = 150 + 40 * i
                set_source(ctx, c)
                circle(ctx, x, y, 20)
                fill(ctx)
            end
        end
        Gtk.showall(win)
    end

    function submitguess!(w)
        if length(currentguess) == length(code)
            g = Guess(code, currentguess)
            push!(guesshistory, g)
            empty!(currentguess)
            guessesused += 1
            draw(can)
            if all(i -> g.code[i] == g.guess[i], 1:length(code))
                saywon!()
            elseif guessesused > maxguesses
                outofguesses!()
            end
        end
    end
    signal_connect(submitguess!, tryguess, :clicked)

    function undolast!(w)
        if length(currentguess) > 0
            pop!(currentguess)
            draw(can)
        end
    end
    signal_connect(undolast!, eraselast, :clicked)

    newgame!(win)
    Gtk.showall(win)
   
    condition = Condition()
    endit(w) = notify(condition)
    signal_connect(endit, win, :destroy)
    showall(win)
    wait(condition)
end

mastermindapp()

Kotlin

Translation of: C++
// version 1.2.51

import java.util.Random

val rand = Random()

class Mastermind {
    private val codeLen: Int
    private val colorsCnt: Int
    private var guessCnt = 0
    private val repeatClr: Boolean

    private val colors: String
    private var combo = ""

    private val guesses = mutableListOf<CharArray>()
    private val results = mutableListOf<CharArray>()

    constructor(codeLen: Int, colorsCnt: Int, guessCnt: Int, repeatClr: Boolean) {
        val color = "ABCDEFGHIJKLMNOPQRST"
        this.codeLen = codeLen.coerceIn(4, 10)
        var cl = colorsCnt
        if (!repeatClr && cl < this.codeLen) cl = this.codeLen
        this.colorsCnt = cl.coerceIn(2, 20)       
        this.guessCnt = guessCnt.coerceIn(7, 20)    
        this.repeatClr = repeatClr
        this.colors = color.take(this.colorsCnt)
    }

    fun play() {
        var win = false
        combo = getCombo()
        while (guessCnt != 0) {
            showBoard()
            if (checkInput(getInput())) {
                win = true
                break
            }
            guessCnt--
        }
        println("\n\n--------------------------------")
        if (win) {
            println("Very well done!\nYou found the code: $combo")
        }
        else {
            println("I am sorry, you couldn't make it!\nThe code was: $combo")
        }
        println("--------------------------------\n")
    }

    private fun showBoard() {
        for (x in 0 until guesses.size) {
            println("\n--------------------------------")
            print("${x + 1}: ")
            for (y in guesses[x]) print("$y ")
            print(" :  ")
            for (y in results[x]) print("$y ")
            val z = codeLen - results[x].size
            if (z > 0) print("- ".repeat(z))
        }
        println("\n")
    }

    private fun getInput(): String {
        while (true) {
            print("Enter your guess ($colors): ")
            val a = readLine()!!.toUpperCase().take(codeLen)          
            if (a.all { it in colors } ) return a
        }
    }

    private fun checkInput(a: String): Boolean {
        guesses.add(a.toCharArray())
        var black = 0
        var white = 0
        val gmatch = BooleanArray(codeLen)
        val cmatch = BooleanArray(codeLen)
        for (i in 0 until codeLen) {
            if (a[i] == combo[i]) {
                gmatch[i] = true
                cmatch[i] = true
                black++
            }
        }
        for (i in 0 until codeLen) {
            if (gmatch[i]) continue
            for (j in 0 until codeLen) {
                if (i == j || cmatch[j]) continue
                if (a[i] == combo[j]) {
                    cmatch[j] = true
                    white++
                    break
                }
            }
        }   
        val r = mutableListOf<Char>()
        r.addAll("X".repeat(black).toList())
        r.addAll("O".repeat(white).toList())    
        results.add(r.toCharArray())
        return black == codeLen
    }

    private fun getCombo(): String {
        val c =  StringBuilder()
        val clr = StringBuilder(colors)
        for (s in 0 until codeLen) {
            val z = rand.nextInt(clr.length)
            c.append(clr[z])
            if (!repeatClr) clr.deleteCharAt(z)
        }
        return c.toString()
    }
}

fun main(args: Array<String>) {
    val m = Mastermind(4, 8, 12, false)
    m.play()
}

Sample input/output (showing last 2 guesses only):

Enter your guess (ABCDEFGH): hcgb

--------------------------------
1: A B C D  :  O - - - 
--------------------------------
2: E F G H  :  X O O - 
--------------------------------
3: E G F A  :  O O - - 
--------------------------------
4: G F E A  :  O O - - 
--------------------------------
5: F H G B  :  X X O - 
--------------------------------
6: F B G C  :  X O - - 
--------------------------------
7: F G A B  :  X O - - 
--------------------------------
8: A H G C  :  X O - - 
--------------------------------
9: G H D B  :  X O O - 
--------------------------------
10: H A G B  :  X X X - 
--------------------------------
11: H C G B  :  X X X - 

Enter your guess (ABCDEFGH): hegb


--------------------------------
Very well done!
You found the code: HEGB
--------------------------------

Lua

Based on C++

math.randomseed( os.time() )
local black, white, none, code = "X", "O", "-"
local colors, codeLen, maxGuess, rept, alpha, opt = 6, 4, 10, false, "ABCDEFGHIJKLMNOPQRST", ""
local guesses, results
function createCode()
    code = ""
    local dic, a = ""
    for i = 1, colors do
        dic = dic .. alpha:sub( i, i )
    end
    for i = 1, codeLen do
        a = math.floor( math.random( 1, #dic ) )
        code = code .. dic:sub( a, a )
        if not rept then
            dic = dic:sub(1, a - 1 ) .. dic:sub( a + 1, #dic )
        end
    end
end
function checkInput( inp )
    table.insert( guesses, inp )
    local b, w, fnd, str = 0, 0, {}, ""
    for bl = 1, codeLen do
        if inp:sub( bl, bl ) == code:sub( bl, bl ) then
            b = b + 1; fnd[bl] = true
        else
            for wh = 1, codeLen do
                if nil == fnd[bl] and wh ~= bl and inp:sub( wh, wh ) == code:sub( bl, bl ) then
                    w = w + 1; fnd[bl] = true
                end
            end
        end
    end
    for i = 1, b do str = str .. string.format( "%s ", black ) end
    for i = 1, w do str = str .. string.format( "%s ", white ) end
    for i = 1, 2 * codeLen - #str, 2 do str = str .. string.format( "%s ", none ) end
    table.insert( results, str )
    return b == codeLen
end
function play()
    local err, win, r = true, false;
    for j = 1, colors do opt = opt .. alpha:sub( j, j ) end
    while( true ) do
        createCode(); guesses, results = {}, {}
        for i = 1, maxGuess do
            err = true;
            while( err ) do
                io.write( string.format( "\n-------------------------------\nYour guess (%s)?", opt ) )
                inp = io.read():upper(); 
                if #inp == codeLen then
                    err = false;
                    for k = 1, #inp do
                        if( nil == opt:find( inp:sub( k, k ) ) ) then 
                            err = true;
                            break;
                        end
                    end
                end
            end
            if( checkInput( inp ) ) then win = true; break
            else
                for l = 1, #guesses do
                    print( string.format( "%.2d: %s : %s", l, guesses[l], results[l] ) )
                end
            end
        end
        if win then print( "\nWell done!" )
        else print( string.format( "\nSorry, you did not crack the code --> %s!", code ) )
        end
        io.write( "Play again( Y/N )? " ); r = io.read()
        if r ~= "Y" and r ~= "y" then break end
    end
end
--[[ entry point ]]---
if arg[1] ~= nil and tonumber( arg[1] ) > 1 and tonumber( arg[1] ) < 21 then colors = tonumber( arg[1] ) end
if arg[2] ~= nil and tonumber( arg[2] ) > 3 and tonumber( arg[2] ) < 11 then codeLen = tonumber( arg[2] ) end
if arg[3] ~= nil and tonumber( arg[3] ) > 6 and tonumber( arg[3] ) < 21 then maxGuess = tonumber( arg[3] ) end
if arg[4] ~= nil and arg[4] == "true" or arg[4] == "false" then rept = ( arg[4] == "true" ) end
play()
Output:
-------------------------------
Your guess (ABCDEF)?bcde
01: BCDE : X X - -

-------------------------------
Your guess (ABCDEF)?bcaf
01: BCDE : X X - -
02: BCAF : X O O -

-------------------------------
Your guess (ABCDEF)?badf
01: BCDE : X X - -
02: BCAF : X O O -
03: BADF : X X O -

-------------------------------
Your guess (ABCDEF)?bafe

Well done!
Play again( Y/N )?

M2000 Interpreter

 
mastermind






Module MasterMind {
	cls #225522, 0
	GetInput=lambda (s as string, min as integer, max as integer) -> {
		do
			print s+"("+min+" - "+max+")";
			Input ":",v%
		until v%>=min and v%<=max
		=v%
	}
	GetInputGuess=lambda (moves as integer, length as integer, max as integer, once as boolean) -> {
		string k, s
		integer j, oldi
		boolean check[max]=false
		pen 15 {print str$(moves,"00")+". ";}
		for i=1 to length
			do
				do
					if oldi=i then beep
					k=ucase$(key$)
					j = asc(k)-64
					oldi=i
				when j<1 or j>max
			when once and check[j]
			pen #99ffbb {print k;}
			if once then check[j]=true
			s+=k
		next
		=s
	}
	DisplayFinal=lambda (a) -> {
		string s
		for i=1 to len(a)-1
			s+=chr$(64+a[i])
		next
		=s
	}
	pen 15
	integer C=GetInput("number of colors", 2, 20)
	integer CL=GetInput("code length", 4, 10)
	integer mn=GetInput("maximum number of guesses", 7, 20)
	if c>=CL then
		boolean rc=GetInput("colors may be repeated in the code", 0, 1)
	else
		boolean rc=true
	end if
	pen #00ff00
	Cls ,0
	integer acc[CL], i
	do
		if rc then
			for i=1 to cl: acc[i]=random(1, C): next
		else
			boolean color[C]
			for i=1 to cl
				do
					acc[i]=random(1, C)
				when color[acc[i]]
				color[acc[i]]=true
			next		
		end if
		string target=DisplayFinal(acc), z, mark
		integer moves=1
		pen 15 {Print "Guess", @(20),"Mark"}
		for i=1 to mn
			z=GetInputGuess(i, CL, C, Not RC)
			if target=z then exit for
			mark=""
			for j=1 to CL
				if acc[j]=asc(mid$(z, j, 1))-64 then
					mark+="X"		
				else.if instr(target, mid$(z, j, 1))>0 then
					mark+="O"
				else
					mark+="-"
				end if
			next
			Print @(20), mark
		next
		print
		if target=z then
			pen 15 {print "Guess Done"}
		else
			print "You loose, secret code was:"+target
		end if
		print "Play again ? (Y - N)"
	Until ucase$(key$)<>"Y"
}
MasterMind

Nim

Translation of: Python
import random, sequtils, strformat, strutils

proc encode(correct, guess: string): string =
  result.setlen(correct.len)
  for i in 0..correct.high:
    result[i] = if correct[i] == guess[i]: 'X' else: (if guess[i] in correct: 'O' else: '-')
  result.join(" ")

proc safeIntInput(prompt: string; minVal, maxVal: Positive): int =
  while true:
    stdout.write prompt
    let userInput = stdin.readLine()
    result = try: parseInt(userInput)
             except ValueError: continue
    if result in minVal..maxVal:
      return


proc playGame() =

  echo "You will need to guess a random code."
  echo "For each guess, you will receive a hint."
  echo "In this hint, X denotes a correct letter, " &
       "and O a letter in the original string but in a different position."
  echo ""

  let numLetters = safeIntInput("Select a number of possible letters for the code (2-20): ", 2, 20)
  let codeLength = safeIntInput("Select a length for the code (4-10): ", 4, 10)
  let letters = "ABCDEFGHIJKLMNOPQRST"[0..<numLetters]
  let code = newSeqWith(codeLength, letters.sample()).join()
  var guesses: seq[string]

  while true:
    echo ""
    stdout.write &"Enter a guess of length {codeLength} ({letters}): "
    let guess = stdin.readLine().toUpperAscii().strip()
    if guess.len != codeLength or guess.anyIt(it notin letters):
      continue
    elif guess == code:
      echo &"\nYour guess {guess} was correct!"
      break
    else:
      guesses.add &"{guesses.len + 1}: {guess.join(\" \")} => {encode(code, guess)}"
    for guess in guesses:
      echo "------------------------------------"
      echo guess
    echo "------------------------------------"


randomize()
playGame()
Output:
You will need to guess a random code.
For each guess, you will receive a hint.
In this hint, X denotes a correct letter, and O a letter in the original string but in a different position.

Select a number of possible letters for the code (2-20): 4
Select a length for the code (4-10): 4

Enter a guess of length 4 (ABCD): ABCD
------------------------------------
1: A B C D => - O - X
------------------------------------

Enter a guess of length 4 (ABCD): BDBD
------------------------------------
1: A B C D => - O - X
------------------------------------
2: B D B D => X X O X
------------------------------------

Enter a guess of length 4 (ABCD): BDDD

Your guess BDDD was correct!

Perl

Translation of: Raku
use List::Util qw(any);

print 'Enter pool size, puzzle size, attempts allowed: '; 
($pool,$length,$tries) = split /\s+/, <>;
$length =  4 if $length eq '' or $length < 3 or $length > 11;
$pool   =  6 if $pool   eq '' or $pool   < 2 or $pool   > 21;
$tries  = 10 if $tries  eq '' or $tries  < 7 or $tries  > 21;

@valid  = sort { -1 + 2*int(rand 2) } ('A' .. 'T')[0..$pool-1];
@puzzle = @valid[0..$length-1];

$black = '●';
$white = '○';

while () {
    header();
    print "$_\n" for @guesses;
    lose() if  @guesses == $tries;
    @guess = get_guess();
    next unless is_valid(@guess);
    $score = score(\@puzzle, \@guess);
    win() if $score eq join ' ', ($black) x $length;
    push @guesses, join(' ', @guess) . ' :: ' . $score;
}

sub score {
    local *puzzle = shift;
    local *guess  = shift;
    my @score;
    for $i (0..$length-1) {
        if    (     $puzzle[$i] eq $guess[$i]) { push @score, $black }
        elsif (any {$puzzle[$i] eq $_} @guess) { push @score, $white }
        else                                   { push @score, '-'    }
    }
    join ' ', reverse sort @score;
}

sub header {
    $num = $tries - @guesses;
    print  "Valid letter, but wrong position: ○ - Correct letter and position: ●\n";
    print  "Guess the $length element sequence containing the letters " . join(', ', sort @valid) . "\n";
    printf "Repeats are not allowed. You have $num guess%s remaining\n", $num > 1 ? 'es' : '';
}

sub get_guess { print 'Your guess?: '; $g = <>; return split /\s*/, uc $g }

sub is_valid { $length == @_ }

sub win  { print 'You win! The correct answer is: ' . join(' ',@puzzle) . "\n"; exit }

sub lose { print 'Too bad, you ran out of guesses. The solution was: ' . join(' ',@puzzle) . "\n"; exit }

Sample output, omitting redundant instructions.

Output:
Valid letter, but wrong position: ○ - Correct letter and position: ●
Guess the 4 element sequence containing the letters A, B, C, D, E, F
Repeats are not allowed. You have 10 guesses remaining
Your guess?: a b c e
A B C E :: ○ ○ ○ -
Your guess?: b a d c
Repeats are not allowed. You have 8 guesses remaining
A B C E :: ○ ○ ○ -
B A D C :: ● ● ○ ○
Your guess?: a b c d
Repeats are not allowed. You have 7 guesses remaining
A B C E :: ○ ○ ○ -
B A D C :: ● ● ○ ○
A B C D :: ○ ○ ○ ○
Your guess?: b d a c
You win! The correct answer is: B D A C

Phix

OTT GUI solution, fully configurable with solver.

-- demo/rosetta/mastermind.exw
constant SET_LIMIT = 1_000_000  -- above this, it uses random sampling.

constant help_text = """
The game of mastermind, with a Knuth solver.

Specify the number of colours (1..20), the code length (1..10), the
number of guesses allowed (1-20), and whether colours can be repeated
(auto-ticked & greyed-out inactive when length>colours).

Note that at the highest settings there are 10,240,000,000,000 possible
answers: the (order n squared) analysis of that is simply not practical, 
as indeed is simply building the initial list of all possible answers, 
and therefore a fixed limit of 1,000,000 has been applied, which also 
just about manages to keep the program responsive. Obviously, should the
actual answer not be among those samples, it cannot possibly find it,
and it will tell you in plain english when that occurs. You can always 
trim the search space back to something more reasonable at any time, and 
still play the game when that limit is breached, with weaker hints. 

Conversely the lowest settings do not make for an interesting game, but
proved quite useful when ironing out some bugs, so were left in.

The Use button (disabled until something useful found) allows you to 
take the best found (so far), displayed at the top of the colours frame. 
Obviously "1/1 (100%)" means that it has deduced the correct answer.
Below that the colours frame shows all available colours, which can be 
individually clicked in any order.

Press Delete or click on the last peg (in the left-hand game frame)
to remove it, before the last one is placed, however once full your
turn is immediately scored and cannot be undone.

New Game, Help, and Exit buttons are assumed to be self-explanatory.
Changing the option settings implicitly triggers a new game, except 
for the number of permitted guesses, pre-game-over. Reducing the
number of guesses can also be used as a means of conceding.

When a correct guess is entered or all guesses have been used the hint 
and colours are replaced with "GAME OVER - YOU WIN/LOSE" under the 
actual answer.
"""
include pGUI.e

Ihandle dlg, colours, codelen, maxgoes, repeats, progress, 
        usehint, game_canvas, colour_canvas
integer ncolours, ncodelen, nmaxgoes
bool brepeats

sequence secret = {},
         hint = {},
         guesses = {{}},
         scores = {}
--
-- note: while the game is ongoing, length(guesses) should always be
--       length(scores)+1; equal lengths is equivalent to game over.
--

function get_score(sequence guess, goal)
integer blacks = 0, -- (right colour & place)
        whites = 0  -- ("" but wrong place)
    for i=1 to length(guess) do
        if guess[i]=goal[i] then
            blacks += 1
            guess[i] = ' '
            goal[i] = ' '
        end if
    end for
    for i=1 to length(guess) do
        if guess[i]!=' ' then
            integer k = find(guess[i],goal)
            if k then
                whites += 1
                goal[k] = ' '
            end if
        end if
    end for
    return {blacks, whites}
end function

function random_set()
-- create the secret code, and/or (when rqd) a SET_LIMIT random sample
    sequence cset = tagset(ncolours),
             res = repeat(0,ncodelen)
    for i=1 to ncodelen do
        integer c = rand(length(cset))
        res[i] = cset[c]
        if not brepeats then
            cset[c..c] = {}
        end if
    end for
    return res
end function

sequence initial_set
atom is_len,    -- logically length(initial_set), except when > SET_LIMIT.
     excluded   -- initialset[1..excluded-1], are not, [excluded..$] are.

procedure create_initial_set()
    is_len = iff(brepeats?power(ncolours,ncodelen):k_perm(ncolours,ncodelen))
    if is_len<=SET_LIMIT then
        --
        -- generate the full set
        --
        initial_set = repeat(0,is_len)
        excluded = is_len+1 -- (ie none)
        sequence next = iff(brepeats?repeat(1,ncodelen):tagset(ncodelen))
        for i=1 to is_len do
            initial_set[i] = next
            for ndx=length(next) to 1 by -1 do
                integer n = next[ndx]
                while n<=ncolours do
                    n += 1
                    if brepeats 
--                  or not find(n,next[1..ndx-1]) then 
                    or not find(n,next) then --(see below)
                        exit
                    end if
                end while
                next[ndx] = n
                if n<=ncolours then
                    if not brepeats then
                        --
                        -- Fill in the rest lowest-first, eg
                        -- in the 4 colours and 4 holes case:
                        --   (start)       (above)       (this)
                        --  {1,2,3,4} --> {1,2,4,_} --> {1,2,4,3}
                        --  {1,2,4,3} --> {1,3,_,_} --> {1,3,2,4}
                        --  ...   (20 other cases omitted)
                        --  {4,3,1,2} --> {4,3,2,_} --> {4,3,2,1}
                        --
                        -- (probably sub-optimal, but insignificant 
                        --  vs. the o(n^2) analysis which follows.)
                        --
                        for j=ndx+1 to length(next) do
                            for k=1 to ncolours do
--                              if not find(k,next[1..j-1]) then
                                if not find(k,next) then --(see below)
                                    next[j] = k
                                    exit
                                end if
                            end for
                        end for
                    end if
                    exit
                end if
                --
                -- technical note: if not brepeats, we are going to
                -- replace all next[ndx..$] later/above anyway, but
                -- replacing with 0 means we can avoid those slices.
                -- The next three all work: 1 is perfect for the
                -- brepeats=true case, but brepeats=false needs the 
                -- above slices, while the 2nd & 3rd are equivalent
                -- the latter is obviously somewhat faster, at the
                -- cost of a wtf?!, without a comment such as this.
                --
--              next[ndx] = 1
--              next[ndx] = iff(brepeats?1:0)
                next[ndx] = brepeats -- (equivalent)
            end for
        end for
    else
        --
        -- generate SET_LIMIT random codes
        -- note that if (as is quite likely) the actual answer is
        -- not present in initial_set, then obviously it cannot
        -- possibly find it!
        --
        initial_set = repeat(0,SET_LIMIT)
        excluded = SET_LIMIT+1  -- (ie none)
        for i=1 to SET_LIMIT do
            initial_set[i] = random_set()
        end for
    end if
end procedure

atom done, is_done, best

function idle_action()
    atom to_do = excluded-1,
         t1 = time()+1
    string samp = iff(is_len=length(initial_set)?"":sprintf(" samples of %,d",{is_len}))
    for i=1 to 100000 do    -- reasonable slice of work
        done += 1
        is_done += (done<excluded)
        sequence guest = initial_set[done],
                 scores = {}, counts = {}
        if not find(guest,guesses) then
            for j=1 to excluded-1 do
                sequence s = get_score(guest,initial_set[j])
                integer k = find(s,scores)
                if k=0 then
                    scores = append(scores,s)
                    counts = append(counts,1)
                else
                    counts[k] += 1
                end if
            end for
            if length(counts)=0 then
                IupSetStrAttribute(progress,"TITLE","[answer not in %,d%s]",{SET_LIMIT,samp})
                return IUP_IGNORE   -- (stop idle)
            end if
            integer k = largest(counts,return_index:=true),
                    ck = counts[k]
            if ck<best then
                best = ck
                hint = guest
                IupSetInt(usehint,"ACTIVE",true)
                IupUpdate(colour_canvas)
            end if
        end if
    
        if done=length(initial_set) then
            IupSetStrAttribute(progress,"TITLE","%,d/%,d%s (100%%)",{is_done,to_do,samp})
            return IUP_IGNORE   -- (stop idle)
        end if
        if time()>t1 then exit end if
    end for
    IupSetStrAttribute(progress,"TITLE","%,d/%,d%s (%d%%)",{is_done,to_do,samp,100*(is_done/to_do)})
    return IUP_DEFAULT
end function
constant idle_action_cb = Icallback("idle_action")

procedure start_idle()
    done = 0
    is_done = 0
    best = length(initial_set)+1
    IupSetGlobalFunction("IDLE_ACTION",idle_action_cb)
end procedure

procedure new_game()
    ncolours = IupGetInt(colours,"VALUE")
    ncodelen = IupGetInt(codelen,"VALUE")
    nmaxgoes = IupGetInt(maxgoes,"VALUE")
    brepeats = IupGetInt(repeats,"VALUE")
    secret = random_set()
    guesses = {{}}
    scores = {}
    hint = {}
    create_initial_set()
    start_idle()
end procedure

constant colour_table = {#e6194b,   -- Red
                         #3cb44b,   -- Green
                         #ffe119,   -- Yellow
                         #4363d8,   -- Blue
                         #f58231,   -- Orange
                         #911eb4,   -- Purple
                         #42d4f4,   -- Cyan
                         #f032e6,   -- Magenta
                         #bfef45,   -- Lime
                         #fabebe,   -- Pink
                         #469990,   -- Teal
                         #e6beff,   -- Lavender
                         #9A6324,   -- Brown
                         #fffac8,   -- Beige
                         #800000,   -- Maroon
                         #aaffc3,   -- Mint
                         #808000,   -- Olive
                         #ffd8b1,   -- Apricot
                         #000075,   -- Navy
                         #a9a9a9}   -- Grey

-- saved in redraw_cb(), for click testing in button_cb():
sequence last_guess = {},
         colour_centres = {}
integer guess_r2 = 0,
        colour_r2 = 0

function redraw_cb(Ihandle ih, integer /*posx*/, integer /*posy*/)
    Ihandle frame = IupGetParent(ih)
    string title = IupGetAttribute(ih,"TITLE")
    if not find(title,{"Game","Colours"}) then ?9/0 end if
    integer {cw,ch} = IupGetIntInt(ih, "DRAWSIZE")
    
    cdCanvas cddbuffer = IupGetAttributePtr(ih,"DBUFFER")
    IupGLMakeCurrent(ih)
    cdCanvasActivate(cddbuffer)
    cdCanvasClear(cddbuffer)

    if title="Game" then
        integer mx = min(floor(cw/(ncodelen*1.5+0.5)),floor(ch/(nmaxgoes+1))),
                diameter = floor(mx/2),
                px = floor((cw-(ncodelen*1.5+0.5)*mx)/2), -- (set margin)
                cy = ch, cx, c, r
        last_guess = {}
        for g=1 to length(guesses) do
            cy -= mx
            cx = px+floor(mx/2)
            for i=1 to 2*ncodelen+1 do
                if i!=ncodelen+1 then
                    if i<=ncodelen then
                        if i<=length(guesses[g]) then
                            c = colour_table[guesses[g][i]]
                            if g=length(guesses) then
                                last_guess = {{cx,ch-cy}}
                            end if
                        else
                            c = CD_GREY
                        end if
                        r = diameter
                    else
                        c = CD_GREY
                        if g<=length(scores) then
                            integer k = i-ncodelen-1,
                                    {b,w} = scores[g]
                            c = iff(k<=b ? CD_BLACK : iff(k<=b+w ? CD_WHITE : CD_GREY))
                        end if
                        r = floor(diameter*0.5)
                    end if
                    cdCanvasSetForeground(cddbuffer,c)
                    cdCanvasSector(cddbuffer, cx, cy, r, r, 0, 360)
                    cdCanvasSetForeground(cddbuffer,CD_DARK_GREY)
                    cdCanvasCircle(cddbuffer, cx, cy, r)
                end if
                cx += iff(i<ncodelen?mx:floor(mx/2))
            end for
        end for
        guess_r2 = floor(diameter*diameter/4)
    elsif title="Colours" then
        integer mx = min(floor(cw/ncodelen),floor(ch/2)),
                r = floor(mx/2),
                px = floor((cw-ncodelen*mx)/2), -- (set margin)
                cy = ch-r, cx, c
        cx = px+floor(mx/2)
        bool active = length(hint)>0
        if length(scores)=nmaxgoes then
            hint = secret
            active = true
        end if
        for i=1 to ncodelen do
            c = iff(active?colour_table[hint[i]]:CD_GREY)
            cdCanvasSetForeground(cddbuffer,c)
            cdCanvasSector(cddbuffer, cx, cy, r, r, 0, 360)
            cdCanvasSetForeground(cddbuffer,CD_DARK_GREY)
            cdCanvasCircle(cddbuffer, cx, cy, r)
            cx += mx
        end for
        if length(scores)=nmaxgoes
        or guesses[$]=secret then
            ch -= floor(mx/2)
            {} = cdCanvasTextAlignment(cddbuffer, CD_CENTER)
            string wl = iff(guesses[$]=secret?"WIN":"LOSE"),
                   msg = sprintf("GAME OVER - YOU %s",{wl})
            cdCanvasText(cddbuffer, cw/2, ch/2, msg) 
        else
            integer ch0 = ch
            ch -= mx
            --
            -- calculate the best nw*nh way to fit all the colours in:
            -- (if nw ends up = ncodelen there is no clear separation
            --  between the hint and the colour table; the start with
            --  ncodelen+1 solves that and looks pretty good to me.)
            --
            integer nw = ncodelen+1,    -- (as above)
                    nh = 1
            while nw*nh<ncolours do
                if (cw/(nw+1))>(ch/(nh+1)) then
                    nw += 1
                else
                    nh += 1
                end if
            end while
            --
            -- now draw all the colours
            --
            mx = min(floor(cw/nw),floor(ch/nh))
            r = floor(mx/2)
            px = floor((cw-nw*mx)/2)
            cx = px+floor(mx/2)
            cy = ch-r
            integer this_row = 0
            colour_centres = repeat(0,ncolours)
            colour_r2 = floor(r*r/4)
            for i=1 to ncolours do
                colour_centres[i] = {cx,ch0-cy}
                c = colour_table[i]
                cdCanvasSetForeground(cddbuffer,c)
                cdCanvasSector(cddbuffer, cx, cy, r, r, 0, 360)
                cdCanvasSetForeground(cddbuffer,CD_DARK_GREY)
                cdCanvasCircle(cddbuffer, cx, cy, r)
                cx += mx
                this_row += 1
                if this_row>=nw then
                    this_row = 0
                    cx = px + floor(mx/2)
                    cy -= mx
                end if
            end for
        end if
    end if
    cdCanvasFlush(cddbuffer)
    return IUP_DEFAULT
end function

function map_cb(Ihandle ih)
    IupGLMakeCurrent(ih)
    atom res = IupGetDouble(NULL, "SCREENDPI")/25.4
    cdCanvas cddbuffer = cdCreateCanvas(CD_GL, "10x10 %g", {res})
    IupSetAttributePtr(ih,"DBUFFER",cddbuffer)
    cdCanvasSetBackground(cddbuffer, CD_PARCHMENT)
    return IUP_DEFAULT
end function

function canvas_resize_cb(Ihandle canvas)
    cdCanvas cddbuffer = IupGetAttributePtr(canvas,"DBUFFER")
    integer {canvas_width, canvas_height} = IupGetIntInt(canvas, "DRAWSIZE")
    atom res = IupGetDouble(NULL, "SCREENDPI")/25.4
    cdCanvasSetAttribute(cddbuffer, "SIZE", "%dx%d %g", {canvas_width, canvas_height, res})
    return IUP_DEFAULT
end function

procedure redraw_all()
    IupUpdate({game_canvas,colour_canvas})
end procedure

procedure undo_move()
-- Called from button_cb and from K_DEL, but latter may be invalid.
    if length(guesses[$])!=0 then
        guesses[$] = guesses[$][1..$-1]
        redraw_all()
    end if
end procedure

procedure add_move(integer i)
    if i!=0 then
        guesses[$] &= i
    end if
    if length(guesses[$])=ncodelen then
        sequence guest = guesses[$],
                 score = get_score(guest,secret)
        scores = append(scores,score)   
        if score!={ncodelen,0}  -- (not all black==game over)
        and length(guesses)<nmaxgoes then
            for i=excluded-1 to 1 by -1 do
                sequence isi = initial_set[i]
                if get_score(guest,isi)!=score then
                    excluded -= 1
                    if excluded!=i then
                        initial_set[i] = initial_set[excluded]
                        initial_set[excluded] = isi -- (swap)
                    end if
                end if
            end for
            guesses = append(guesses,{})
            hint = {}
            IupSetAttribute(progress,"TITLE","-")
            IupSetInt(usehint,"ACTIVE",false)
            start_idle()
        end if
    end if
    redraw_all()
end procedure

function usehint_cb(Ihandle /*usehint*/)
    guesses[$] = hint
    add_move(0)
    return IUP_DEFAULT
end function

function button_cb(Ihandle canvas, integer button, pressed, x, y, atom /*pStatus*/)
    Ihandle frame = IupGetParent(canvas)
    string title = IupGetAttribute(frame,"TITLE")
    if not find(title,{"Game","Colours"}) then ?9/0 end if
    if button=IUP_BUTTON1 and not pressed then      -- (left button released)
        {sequence centres, integer r2} = iff(title="Game"?{last_guess,guess_r2}
                                                         :{colour_centres,colour_r2})
        for i=1 to length(centres) do
            integer {cx,cy} = sq_sub(centres[i],{x,y})
            if (cx*cx+cy*cy)<=r2 then
                if title="Game" then
                    undo_move()
                else
                    add_move(i)
                end if
                exit
            end if
        end for
    end if
    return IUP_CONTINUE
end function

function new_game_cb(Ihandle /*ih*/)
    new_game()
    redraw_all()
    return IUP_DEFAULT
end function

function exit_cb(Ihandle /*ih*/)
    return IUP_CLOSE
end function
constant cb_exit = Icallback("exit_cb")

function help_cb(Ihandln /*ih*/)
    IupMessage("Mastermind",help_text)
    return IUP_DEFAULT
end function

function key_cb(Ihandle /*dlg*/, atom c)
    if c=K_ESC then return IUP_CLOSE end if
    if c=K_F1 then return help_cb(NULL) end if
    if find(c,{K_DEL,K_BS}) then undo_move() end if
    return IUP_CONTINUE
end function

function valuechanged_cb(Ihandle ih)
    ncolours = IupGetInt(colours,"VALUE")
    ncodelen = IupGetInt(codelen,"VALUE")
    nmaxgoes = IupGetInt(maxgoes,"VALUE")
    IupSetInt(repeats,"ACTIVE",ncodelen<=ncolours)
    if ncodelen>ncolours then
        IupSetInt(repeats,"VALUE",true)
    end if
    brepeats = IupGetInt(repeats,"VALUE")
    if ih!=maxgoes
    or length(scores)=length(guesses) then  -- (game over)
        new_game()
    elsif nmaxgoes<=length(scores) then
        -- (signal/force game over state)
        guesses = guesses[1..length(scores)]
    end if
    redraw_all()
    return IUP_DEFAULT
end function
constant cb_valuechanged = Icallback("valuechanged_cb")

procedure main()
    IupOpen()
 
    colours = IupText("SPIN=Yes, SPINMIN=1, SPINMAX=20, VALUE=6, RASTERSIZE=34x")
    codelen = IupText("SPIN=Yes, SPINMIN=1, SPINMAX=10, VALUE=4, RASTERSIZE=34x")
    maxgoes = IupText("SPIN=Yes, SPINMIN=1, SPINMAX=20, VALUE=7, RASTERSIZE=34x")
    repeats = IupToggle("Repeatable?","VALUE=YES, RIGHTBUTTON=YES, PADDING=5x4")
    progress = IupLabel("-","EXPAND=HORIZONTAL, PADDING=5x4")
    usehint = IupButton("Use",Icallback("usehint_cb"),"PADDING=5x4, ACTIVE=NO")
    game_canvas = IupGLCanvas("RASTERSIZE=200x")
    colour_canvas = IupGLCanvas("RASTERSIZE=x200")
    Ihandle newgame = IupButton("New Game",Icallback("new_game_cb"),"PADDING=5x4"),
            help = IupButton("Help (F1)",Icallback("help_cb"),"PADDING=5x4"),
            quit = IupButton("E&xit",Icallback("exit_cb"),"PADDING=5x4"),
            vbox = IupVbox({IupHbox({IupLabel("Colours (1-20)","PADDING=5x4"),colours}),
                            IupHbox({IupLabel("Code Length (1-10)","PADDING=5x4"),codelen}),
                            IupHbox({IupLabel("Guesses (1-20)","PADDING=5x4"),maxgoes}),
                            IupHbox({repeats},"MARGIN=10x5"),
                            IupHbox({progress}),
                            IupHbox({usehint,newgame,help,quit})},"MARGIN=5x5"),
            game_frame = IupFrame(IupHbox({game_canvas},"MARGIN=3x3"),"TITLE=Game"),
            option_frame = IupFrame(vbox,"TITLE=Options"),
            colour_frame = IupFrame(colour_canvas,"TITLE=Colours"),
            full = IupHbox({game_frame,IupVbox({option_frame,colour_frame})})
    IupSetCallbacks({colours,codelen,maxgoes,repeats}, {"VALUECHANGED_CB", cb_valuechanged})
    IupSetCallbacks({game_canvas,colour_canvas}, {"ACTION", Icallback("redraw_cb"),
                                                  "MAP_CB", Icallback("map_cb"),
                                                  "RESIZE_CB", Icallback("canvas_resize_cb"),
                                                  "BUTTON_CB", Icallback("button_cb")})
    dlg = IupDialog(IupHbox({full},"MARGIN=3x3"),"TITLE=Mastermind")
    IupSetCallback(dlg, "K_ANY", Icallback("key_cb"))
    IupSetAttributeHandle(dlg,"DEFAULTENTER", usehint)

    new_game()

    IupShowXY(dlg,IUP_CENTER,IUP_CENTER)
    IupSetAttribute(dlg, "RASTERSIZE", NULL)
    IupSetStrAttribute(dlg, "MINSIZE", IupGetAttribute(dlg,"RASTERSIZE"))
    IupMainLoop()
    IupClose()
end procedure
main()

Prolog

mastermind :- mastermind(7, 4, 8, no_duplicates).

mastermind(Colours, Length, Guesses, Duplicates) :-
	between(2, 20, Colours),
	between(4, 10, Length),
	between(7, 20, Guesses),
	member(Duplicates, [allow_duplicates, no_duplicates]),

	create_board(Colours, Length, Duplicates, Board),
	intro(Colours, Length, Duplicates),
	play(board(Board, Length, Colours, Guesses), [], 0), !.

intro(Colours, Length, Duplicates) :-
	format('Guess the code!~n'),
	format('There are ~p character types, and ~p letters to guess~n',
	    [Colours, Length]),
	Duplicates = allow_duplicates
	-> format('Duplicates are allowed~n~n')
	; format('Duplicates are not allowed~n~n').

/* Create the combination to be guessed */
create_board(Colours, Length, Duplicates, Board) :-
	length(Board, Length),
	valid_char_list(Colours, CharSet),
	repeat,
	maplist(random_alpha(CharSet), Board),
	check_for_duplicates(Board, Duplicates).

check_for_duplicates(_, allow_dupicates).
check_for_duplicates(Board, no_duplicates) :- is_set(Board).

/* Main loop - get the player guess and print out status */
play(board(Board,_,_,MaxGuesses), _, MaxGuesses) :-
	write('Sorry, You failed to guess in time...!\nThe code was : '),
	maplist(write, Board),
	nl.
play(BoardData, PrevGuesses, GuessNum) :-
	BoardData = board(_, Length, Colours, MaxGuesses),
	GuessNum < MaxGuesses,
	ReportedGuess is GuessNum + 1,
	format('Guess #~p of #~p: ', [ReportedGuess, MaxGuesses]),
	get_player_guess(Length, Colours, Guess),
	evaluate_and_print_result(BoardData, PrevGuesses, ReportedGuess, Guess).

evaluate_and_print_result(board(Board,_,_,_), _, _,Board) :-
	format('Well done! You Guessed Correctly.~n').
evaluate_and_print_result(BoardData, PrevGuesses, NextGuessNum, Guess) :-
	BoardData = board(Board, _, _, _),
	dif(Board, Guess),
	match_guess_to_board(Board, Guess, Diffs),
	append(PrevGuesses, [guess(NextGuessNum, Guess, Diffs)], Guesses),
	maplist(print_guess, Guesses),
	play(BoardData, Guesses, NextGuessNum).

/* Get the player guess and validate that it matches the rules */
get_player_guess(Length, Colours, Guess) :-
	repeat,
	read_line_to_string(user_input, Line),
	string_chars(Line, Guess),

	% validate the correct number of items have been entered
	length(Guess, Length),

	% validate that all the characters are valid for the number of colours
	valid_char_list(Colours, ValidCharSet),
	subset(Guess, ValidCharSet).

/* Predicates to figure out how many places are correct */
match_guess_to_board(Board, Guess, Matches) :-
	maplist(guess_differences(Board), Board, Guess, Differences),
	sort(0, @>=, Differences, Matches).

% Same position, same type
guess_differences(_Board, B, B, 'X').
% Same type, different position
guess_differences(Board, B, G, 'O') :- dif(B, G), member(G, Board).
% Type not on board
guess_differences(Board, B, G, '-') :- dif(B, G), \+ member(G, Board).

/* Print out the current progress */
print_guess(guess(NextGuessNumber, Guess, Differences))	:-
	format('~w: ', NextGuessNumber),
	maplist(format('~w '), Guess),
	format(' : '),
	maplist(format('~w '), Differences),
	nl.

/* Utils */
alpha_chars([a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t]).

valid_char_list(Colours, CharSet) :-
	alpha_chars(AllChars),
	truncate_list(AllChars, Colours, CharSet).

random_alpha(AllChars, RandomMember) :- random_member(RandomMember, AllChars).

truncate_list(_, 0, []).
truncate_list([A|T], N, [A|R]) :-
	N > 0,
	N1 is N - 1,
	truncate_list(T, N1, R).
Output:
1 ?- mastermind.
Guess the code!
There are 7 character types, and 4 letters to guess
Duplicates are not allowed

Guess #1 of #8: abcd
1: a b c d  : X O O -
Guess #2 of #8: acbe
1: a b c d  : X O O -
2: a c b e  : X O - -
Guess #3 of #8: fgab
1: a b c d  : X O O -
2: a c b e  : X O - -
3: f g a b  : O O - -
Guess #4 of #8: cdfg
1: a b c d  : X O O -
2: a c b e  : X O - -
3: f g a b  : O O - -
4: c d f g  : X X O -
Guess #5 of #8: cdfb
1: a b c d  : X O O -
2: a c b e  : X O - -
3: f g a b  : O O - -
4: c d f g  : X X O -
5: c d f b  : X X O -
Guess #6 of #8: cdaf
1: a b c d  : X O O -
2: a c b e  : X O - -
3: f g a b  : O O - -
4: c d f g  : X X O -
5: c d f b  : X X O -
6: c d a f  : X O O O
Guess #7 of #8: acdf
1: a b c d  : X O O -
2: a c b e  : X O - -
3: f g a b  : O O - -
4: c d f g  : X X O -
5: c d f b  : X X O -
6: c d a f  : X O O O
7: a c d f  : X O O O
Guess #8 of #8: adfc
Well done! You Guess Correctly.
true.

Python

Works with: cpython version 3.7.3

Tested in Python 3.7.3. Includes input verification.

import random


def encode(correct, guess):
    output_arr = [''] * len(correct)

    for i, (correct_char, guess_char) in enumerate(zip(correct, guess)):
        output_arr[i] = 'X' if guess_char == correct_char else 'O' if guess_char in correct else '-'

    return ''.join(output_arr)


def safe_int_input(prompt, min_val, max_val):
    while True:
        user_input = input(prompt)

        try:
            user_input = int(user_input)
        except ValueError:
            continue

        if min_val <= user_input <= max_val:
            return user_input


def play_game():
    print("Welcome to Mastermind.")
    print("You will need to guess a random code.")
    print("For each guess, you will receive a hint.")
    print("In this hint, X denotes a correct letter, and O a letter in the original string but in a different position.")
    print()

    number_of_letters = safe_int_input("Select a number of possible letters for the code (2-20): ", 2, 20)
    code_length = safe_int_input("Select a length for the code (4-10): ", 4, 10)

    letters = 'ABCDEFGHIJKLMNOPQRST'[:number_of_letters]
    code = ''.join(random.choices(letters, k=code_length))
    guesses = []

    while True:
        print()
        guess = input(f"Enter a guess of length {code_length} ({letters}): ").upper().strip()

        if len(guess) != code_length or any([char not in letters for char in guess]):
            continue
        elif guess == code:
            print(f"\nYour guess {guess} was correct!")
            break
        else:
            guesses.append(f"{len(guesses)+1}: {' '.join(guess)} => {' '.join(encode(code, guess))}")

        for i_guess in guesses:
            print("------------------------------------")
            print(i_guess)
        print("------------------------------------")


if __name__ == '__main__':
    play_game()
Output:
Welcome to Mastermind.
You will need to guess a random code.
For each guess, you will receive a hint.
In this hint, X denotes a correct letter, and O a letter in the original string but a different position.

Select a number of possible letters for the code (2-20): 4
Select a length for the code (4-10): 4

*omitted first guesses*

Enter a guess of length 4 (ABCD): cdaa
------------------------------------
1: A A B B => O O - -
------------------------------------
2: C D A A => O X X O
------------------------------------

Enter a guess of length 4 (ABCD): ddac

Your guess DDAC was correct!

Raku

(formerly Perl 6)

Works with: Rakudo version 2017.01

By default, plays classic Mastermind using letters in place of colors. ( 4 chosen from 6, no repeats, 10 guess limit. ) Pass in parameters to modify the game. Enter a string of --length (default 4) letters with or without spaces. Guesses accept lower or upper case.

sub MAIN (
    Int :$colors  where 1 < * < 21 = 6,  Int :$length  where 3 < * < 11 = 4,
    Int :$guesses where 7 < * < 21 = 10, Bool :$repeat = False
  ) {
    my @valid = ('A' .. 'T')[^$colors];
    my $puzzle = $repeat ?? @valid.roll($length) !! @valid.pick($length);
    my @guesses;

    my $black = '●';
    my $white = '○';

    loop {
        clearscr();
        say header();
        printf " %{$length * 2}s :: %s\n", @guesses[$_][0], @guesses[$_][1] for ^@guesses;
        say '';
        lose() if @guesses == $guesses;
        my $guess = get-guess();
        next unless $guess.&is-valid;
        my $score = score($puzzle, $guess);
        win() if $score eq ($black xx $length).join: ' ';
        @guesses.push: [$guess, $score];
    }

    sub header {
        my $num = $guesses - @guesses;
        qq:to/END/;
        Valid letter, but wrong position: ○ - Correct letter and position: ●
        Guess the {$length} element sequence containing the letters {@valid}
        Repeats are {$repeat ?? '' !! 'not '}allowed. You have $num guess{ $num == 1 ?? '' !! 'es'} remaining.
        END
    }

    sub score ($puzzle, $guess) {
        my @score;
        for ^$length {
            if $puzzle[$_] eq $guess[$_] {
                @score.push: $black;
            }
            elsif $puzzle[$_] eq any(@$guess) {
                @score.push: $white;
            }
            else {
                @score.push('-');
            }
        }
        @score.sort.reverse.join: ' ';
    }

    sub clearscr { $*KERNEL ~~ /'win32'/ ?? run('cls') !! run('clear') }

    sub get-guess { (uc prompt 'Your guess?: ').comb(/@valid/) }

    sub is-valid (@guess) { so $length == @guess }

    sub win  { say 'You Win! The correct answer is: ', $puzzle; exit }

    sub lose { say 'Too bad, you ran out of guesses. The solution was: ', $puzzle; exit }
}
Sample output:
Valid letter, but wrong position: ○ - Correct letter and position: ●
Guess the 4 element sequence containing the letters A B C D E F
Repeats are not allowed. You have 5 guesses remaining.

  A B C D :: ○ ○ ○ -
  C A B E :: ● ○ ○ -
  D A E F :: ● ○ - -
  B A E C :: ● ○ ○ -
  D E B C :: ○ ○ ○ ○

Your guess?: cdeb
You Win! The correct answer is: (C D E B)

REXX

More checks could have been added   (for illegal inputs and illegal options).

/*REXX pgm scores  mastermind  game with a human  or  CBLFs (Carbon Based Life Forms).  */
parse arg let wid mxG oRep seed _                /*obtain optional arguments from the CL*/
      arg  .   .   .   rep .                     /*get uppercase 4th argument  "   "  " */
if let=='' | let==","  then let= 20              /*Not specified?  Then use the default.*/
if wid=='' | wid==","  then wid=  4              /* "      "         "   "   "     "    */
if mxG=='' | mxG==","  then mxG= 20              /* "      "         "   "   "     "    */
if rep=='' | rep==","  then rep=  0              /* "      "         "   "   "     "    */
if datatype(seed,'W')  then call random ,,seed   /*use a seed for random repeatability. */
if abbrev(  'REPEATSALLOWED',rep,3)  then rep=1  /*allow an abbreviated option for REP. */
if abbrev('NOREPEATSALLOWED',rep,3)  then rep=0  /*  "    "      "         "    "   "   */
call vet   arg(),     'args'                     /*Vet the number of arguments entered. */  /*◄■■■■■■ optional vetting.*/
call vet     let,  'letters', 2, 20              /* "   "     "    " letters in the code*/  /*◄■■■■■■ optional vetting.*/
call vet     wid,    'width', 4, 10              /* "   "     "    " the width of code. */  /*◄■■■■■■ optional vetting.*/
call vet     mxG, 'maxGuess', 7, 20              /* "   "     "    " maximum guesses.   */  /*◄■■■■■■ optional vetting.*/
call vet     rep,      'REP', 0, 1e8             /* "   "   value if repeats are allowed*/  /*◄■■■■■■ optional vetting.*/
call gen;                                        yourG= 'Your guess must be exactly '
                                                 youve= "You've already tried that guess "
        do prompt=0  by 0  until xx==wid;   say  /*play until guessed or QUIT is entered*/
        say id 'Please enter a guess with '   wid  ' letters                   [or Quit]:'
        pull g;   g=space(g,0);  L=length(g);     if abbrev('QUIT',g,1)  then exit 0
        if L\==wid  then do;  say id '***error***'  yourG wid  " letters.";  iterate;  end
        call dups                                /*look through the history log for dups*/
        q=?;      XX=0;      OO=0;     try=try+1 /*initialize some REXX vars;  bump TRY.*/

             do j=1  for L;  if substr(g,j,1) \== substr(q,j,1)  then iterate    /*hit? */
             xx=xx+1;    q=overlay('▒', q, j)    /*bump the  XX  correct   count.       */
             end   /*j*/                         /* [↑]  XX  correct count; scrub guess.*/

             do k=1  for L;   _=substr(g, k, 1)  /*process the count for  "spots".      */
             if pos(_, q)==0  then iterate       /*is this  (spot)  letter in the code? */
             oo=oo+1;       q=translate(q, , _)  /*bump the  OO  spot count.            */
             end   /*k*/                         /* [↑]  OO  spot count;  & scrub guess.*/
        say
        @.try=id  right('guess'  try, 11)     '  ('mxG       "is the max):"    g   '──►' ,
                                      copies('X', xx)copies("O", oo)copies('-', wid-xx-oo)
        call hist
        if try==mxG  then do;  say;      say id   "you've used the maximum guesses:"   mxG
                               say;      say id   "The code was: "   ?;    say;     exit 1
                          end
        end   /*prompt*/
say;                           say "          ┌─────────────────────────────────────────┐"
                               say "          │                                         │"
                               say "          │  Congratulations, you've guessed it !!  │"
                               say "          │                                         │"
                               say "          └─────────────────────────────────────────┘"
exit 0                                           /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
dups:    do h=1  for try;  if g\=word(@.h, 8)  then iterate   /*any duplicated guesses? */
         say;  say id youve  " (guess number" h').'; iterate prompt; end  /*h*/;    return
/*──────────────────────────────────────────────────────────────────────────────────────*/
gen:  if rep==0  then reps= 'no'                 /*create a literal for the prompt msg. */
                 else reps=
      @abc= 'QWERTYUIOPASDFGHJKLZXCVBNM'         /*capital letters used for random code.*/
      id='────────';  try=0;  L@abc=length(@abc) /*identifier in front of msg from here.*/
      ?=
          do  until  length(?)==wid              /*gen random codes 'til there's enough.*/
          r=substr(@abc, random(1, L@abc), 1)    /*generate a random letter, 1 at a time*/
          if \rep & pos(r, ?)\==0  then iterate  /*maybe  don't  allow a repeated digit.*/
          ?=? || r; if ?=='QUIT'&let==4  then ?= /*append random letter; ··· except this*/
          end   /*until*/                        /* [↑]  builds a unique  N-letter code.*/
      say
      say id 'A random code of '   wid   "letters  (out of a possible "  let  ' letters) '
      say id 'has been generated   (with'    reps    "repeats)."
      return
/*──────────────────────────────────────────────────────────────────────────────────────*/
hist:    do hist=1  for try;  say @.hist;  end;   return         /*show "guess" history.*/
s:    if arg(1)==1  then return '';      return "s"              /*a simpler pluraizer. */
ser:  say;  say;    say '***error***'   arg(1);     say;   say;         exit 13
/*──────────────────────────────────────────────────────────────────────────────────────*/  /*◄■■■■■■ optional vetting.*/
vet:  parse arg val,?,mn,mx                      /*vet (validate) a specified argument. */  /*◄■■■■■■ optional vetting.*/
      if ?=="args" & (val>1 | _\='')  then call ser "Too many arguments specified. "  _     /*◄■■■■■■ optional vetting.*/
      if ?=="args"       then return                                                        /*◄■■■■■■ optional vetting.*/
      if \datatype(val, 'N')          then call ser ? "isn't numeric: "               val   /*◄■■■■■■ optional vetting.*/
      if \datatype(val, 'W')          then call ser ? "isn't an integer: "            val   /*◄■■■■■■ optional vetting.*/
      if val < mn                     then call ser ? "has a value less than "        mn    /*◄■■■■■■ optional vetting.*/
      if val > mx                     then call ser ? "has a value greater than "     mx    /*◄■■■■■■ optional vetting.*/
      if ?=='REP' & \datatype(val,W)  then call ser "Value for REPEATS isn't valid: " oRep  /*◄■■■■■■ optional vetting.*/
      return 1

output

──────── A random code of  4 letters  (out of a possible  20  letters)
──────── has been generated   (with no repeats).

──────── Please enter a guess with  4  letters                   [or Quit]:
abcd                  ◄■■■■■■ user input

────────     guess 1   (20 is the max): ABCD ──► ----

──────── Please enter a guess with  4  letters                   [or Quit]:
efgh                  ◄■■■■■■ user input

────────     guess 1   (20 is the max): ABCD ──► ----
────────     guess 2   (20 is the max): EFGH ──► ----

──────── Please enter a guess with  4  letters                   [or Quit]:
ijkl                  ◄■■■■■■ user input

────────     guess 1   (20 is the max): ABCD ──► ----
────────     guess 2   (20 is the max): EFGH ──► ----
────────     guess 3   (20 is the max): IJKL ──► O---

──────── Please enter a guess with  4  letters                   [or Quit]:
mnop                  ◄■■■■■■ user input

     ···············································
     ·    (Some of the output has been elided.)    ·
     ···············································

──────── Please enter a guess with  4  letters                   [or Quit]:
yinp                  ◄■■■■■■ user input

────────     guess 1   (20 is the max): ABCD ──► ----
────────     guess 2   (20 is the max): EFGH ──► ----
────────     guess 3   (20 is the max): IJKL ──► O---
────────     guess 4   (20 is the max): MNOP ──► XO--
────────     guess 5   (20 is the max): WXYZ ──► O---
────────     guess 6   (20 is the max): LKHI ──► O---
────────     guess 7   (20 is the max): PONM ──► XO--
────────     guess 8   (20 is the max): ZYXW ──► O---
────────     guess 9   (20 is the max): YZWX ──► X---
────────    guess 10   (20 is the max): MOPN ──► OO--
────────    guess 11   (20 is the max): OMPN ──► OO--
────────    guess 12   (20 is the max): LKJI ──► O---
────────    guess 13   (20 is the max): JILK ──► X---
────────    guess 14   (20 is the max): YINP ──► XXXX

          ┌─────────────────────────────────────────┐
          │                                         │
          │  Congratulations, you've guessed it !!  │
          │                                         │
          └─────────────────────────────────────────┘

Ring

# Project : Mastermind

colors = ["A", "B", "C", "D"]
places = list(2)
mind = list(len(colors))
rands = list(len(colors))
master = list(len(colors))
test = list(len(colors))
guesses  = 7
repeat = false
nr = 0

if repeat 
   for n = 1 to len(colors)
        while true
                  rnd = random(len(colors)-1) + 1
                  if rands[rnd] != 1
                     mind[n] = rnd
                     rands[rnd] = 1
                    exit
                  ok
        end     
   next
else
   for n = 1 to len(colors)
        rnd = random(len(colors)-1) + 1
        mind[n] = rnd
    next
ok

for n = 1 to len(colors)
      master[n] = char(64+mind[n])
next
while true
         for p = 1 to len(places)
               places[p] = 0
         next
         nr = nr + 1
         see "Your guess (ABCD)? "
         give testbegin
         for d = 1 to len(test)
               test[d] = testbegin[d]
         next 
         flag = 1
         for n = 1 to len(test)
               if upper(test[n]) != master[n]
                  flag = 0
               ok
         next
         if flag = 1
            exit
         else
            for x = 1 to len(master)
                  if upper(test[x]) = master[x]
                      places[1] = places[1] + 1
                  ok                  
            next
            mastertemp = master
            for p = 1 to len(test)
                  pos = find(mastertemp, upper(test[p]))
                  if pos > 0 
                     del(mastertemp, pos)
                     places[2] = places[2] + 1
                  ok
            next 
         ok
         place1 = places[1] 
         place2 = places[2] - place1
         place3 = len(master) - (place1 + place2)
         showresult(test, place1, place2, place3)
         if nr = guesses
            exit
         ok
end
see "Well done!" + nl
see "End of game" + nl

func showresult(test, place1, place2, place3)
        see "" + nr + " : " 
        for r = 1 to len(test)
             see test[r]
        next
        see " : "
        for n1 = 1 to place1
              see "X" + " "
        next
        for n2 = 1 to place2
              see "O" + " "
        next
        for n3 = 1 to place3
              see "-" + " "
        next
        see nl

Output:

Your guess (ABCD)? BCDA
1 : BCDA : X X O - 
Your guess (ABCD)? BCDB
2 : BCDB : X X X - 
Your guess (ABCD)? BCBB
3 : BCBB : X X X - 
Your guess (ABCD)? BCAB
Well done!
End of game

Rust

Library: rand
extern crate rand;

use rand::prelude::*;
use std::io;

fn main() {
    let mut input_line = String::new();
    let colors_n;
    let code_len;
    let guesses_max;
    let colors_dup;

    loop {
        println!("Please enter the number of colors to be used in the game (2 - 20): ");
        input_line.clear();
        io::stdin()
            .read_line(&mut input_line)
            .expect("The read line failed.");
        match (input_line.trim()).parse::<i32>() {
            Ok(n) => {
                if n >= 2 && n <= 20 {
                    colors_n = n;
                    break;
                } else {
                    println!("Outside of range (2 - 20).");
                }
            }
            Err(_) => println!("Invalid input."),
        }
    }
    let colors = &"ABCDEFGHIJKLMNOPQRST"[..colors_n as usize];

    println!("Playing with colors {}.\n", colors);

    loop {
        println!("Are duplicated colors allowed in the code? (Y/N): ");
        input_line.clear();
        io::stdin()
            .read_line(&mut input_line)
            .expect("The read line failed.");
        if ["Y", "N"].contains(&&input_line.trim().to_uppercase()[..]) {
            colors_dup = input_line.trim().to_uppercase() == "Y";
            break;
        } else {
            println!("Invalid input.");
        }
    }
    println!(
        "Duplicated colors {}allowed.\n",
        if colors_dup { "" } else { "not " }
    );
    loop {
        let min_len = if colors_dup { 4 } else { 4.min(colors_n) };
        let max_len = if colors_dup { 10 } else { 10.min(colors_n) };
        println!(
            "Please enter the length of the code ({} - {}): ",
            min_len, max_len
        );
        input_line.clear();
        io::stdin()
            .read_line(&mut input_line)
            .expect("The read line failed.");
        match (input_line.trim()).parse::<i32>() {
            Ok(n) => {
                if n >= min_len && n <= max_len {
                    code_len = n;
                    break;
                } else {
                    println!("Outside of range ({} - {}).", min_len, max_len);
                }
            }
            Err(_) => println!("Invalid input."),
        }
    }
    println!("Code of length {}.\n", code_len);
    loop {
        println!("Please enter the number of guesses allowed (7 - 20): ");
        input_line.clear();
        io::stdin()
            .read_line(&mut input_line)
            .expect("The read line failed.");
        match (input_line.trim()).parse::<i32>() {
            Ok(n) => {
                if n >= 7 && n <= 20 {
                    guesses_max = n;
                    break;
                } else {
                    println!("Outside of range (7 - 20).");
                }
            }
            Err(_) => println!("Invalid input."),
        }
    }
    println!("{} guesses allowed.\n", guesses_max);

    let mut rng = rand::thread_rng();
    let mut code;
    if colors_dup {
        code = (0..code_len)
            .map(|_| ((65 + rng.gen_range(0, colors_n) as u8) as char))
            .collect::<Vec<_>>();
    } else {
        code = colors.chars().collect::<Vec<_>>();
        code.shuffle(&mut rng);
        code = code[..code_len as usize].to_vec();
    }
    //code = vec!['J', 'A', 'R', 'D', 'A', 'N', 'I'];
    //println!("Secret code: {:?}", code);
    let mut guesses: Vec<(String, String)> = vec![];
    let mut i = 1;
    loop {
        println!("Your guess ({}/{})?: ", i, guesses_max);
        input_line.clear();
        io::stdin()
            .read_line(&mut input_line)
            .expect("The read line failed.");
        let mut guess = input_line.trim().to_uppercase();
        if guess.len() as i32 > code_len {
            guess = guess[..code_len as usize].to_string();
        }
        let guess_v = guess.chars().collect::<Vec<char>>();
        let res = evaluate(&code, &guess_v);
        guesses.push((guess, res.clone()));
        let width = 8 + guesses_max.to_string().len() + code_len as usize * 2;
        println!("{}", "-".repeat(width));
        for (i, guess) in guesses.iter().enumerate() {
            let line = format!(
                " {:w1$} : {:w2$} : {:w2$} ",
                i + 1,
                guess.0,
                guess.1,
                w1 = guesses_max.to_string().len(),
                w2 = code_len as usize
            );
            println!("{}", line);
        }
        println!("{}", "-".repeat(width));
        if res == "X".repeat(code_len as usize) {
            println!("You won! Code: {}", code.into_iter().collect::<String>());
            break;
        }
        i += 1;
        if i > guesses_max {
            println!("You lost. Code: {}", code.into_iter().collect::<String>());
            break;
        }
    }
}

fn evaluate(code: &[char], guess: &[char]) -> String {
    let mut res: Vec<char> = vec![];
    for i in 0..guess.len() {
        if guess[i] == code[i] {
            res.push('X');
        } else if code.contains(&guess[i]) {
            res.push('O');
        } else {
            res.push('-');
        }
    }
    res.sort_by(|a, b| b.cmp(a));
    res.into_iter().collect()
}
Output:
Please enter the number of colors to be used in the game (2 - 20):
20
Playing with colors ABCDEFGHIJKLMNOPQRST.

Are duplicated colors allowed in the code? (Y/N):
n
Duplicated colors not allowed.

Please enter the length of the code (4 - 10):
10
Code of length 10.

Please enter the number of guesses allowed (7 - 20):
20
20 guesses allowed.

Your guess (1/20)?:
abcdefghi
------------------------------
  1 : ABCDEFGHI  : OOOOOO---
------------------------------
<...>
Your guess (20/20)?:
ipgecnmhdk
------------------------------
  1 : ABCDEFGHI  : OOOOOO---
  2 : ABCDE      : OOO--
  3 : ABC        : O--
  4 : DEBF       : OO--
  5 : DEAG       : OOO-
  6 : DEAH       : OOO-
  7 : DEAGH      : OOOO-
  8 : DEGHI      : XOOOO
  9 : JKLMN      : OOO--
 10 : JKL        : O--
 11 : K          : O
 12 : DEGHIK     : XOOOOO
 13 : MN         : OO
 14 : OPQ        : X--
 15 : QRS        : ---
 16 : PT         : O-
 17 : PEGHIKCMND : XOOOOOOOOO
 18 : HKMNICDPEG : OOOOOOOOOO
 19 : EGNHKMPDCI : OOOOOOOOOO
 20 : IPGECNMHDK : XXXXXXXXOO
------------------------------
You lost. Code: IPGECHMNDK

SQL

    -- Create Table
    -- Distinct combination
    --- R :Red, B :Blue, G: Green, V: Violet, O: Orange, Y: Yellow
    DROP TYPE IF EXISTS color cascade;CREATE TYPE color AS ENUM ('R', 'B', 'G', 'V', 'O', 'Y');

    DROP TABLE IF EXISTS guesses cascade ; CREATE TABLE guesses (
        first color,
        second color,
        third color ,
        fourth color
    );
    CREATE TABLE mastermind () inherits (guesses);

    INSERT INTO mastermind values ('G', 'B', 'R', 'V');


    INSERT INTO guesses values ('Y', 'Y', 'B', 'B');
    INSERT INTO guesses values ('V', 'R', 'R', 'Y');
    INSERT INTO guesses values ('G', 'V', 'G', 'Y');
    INSERT INTO guesses values ('R', 'R', 'V', 'Y');
    INSERT INTO guesses values ('B', 'R', 'G', 'V');
    INSERT INTO guesses values ('G', 'B', 'R', 'V');


    --- Matches Black
    CREATE OR REPLACE FUNCTION check_black(guesses,  mastermind) RETURNS integer AS $$
        SELECT (
            ($1.first  = $2.first)::int +
            ($1.second  = $2.second)::int +
            ($1.third = $2.third)::int +
            ($1.fourth = $2.fourth)::int
        );
    $$ LANGUAGE SQL;

    --- Matches White
    CREATE OR REPLACE FUNCTION check_white(guesses,  mastermind) RETURNS integer AS $$
        SELECT (
            case when ($1.first = $2.first) then 0 else 0 end +
            case when ($1.second = $2.second) then 0 else 0 end +
            case when ($1.third = $2.third)  then 0 else 0 end +
            case when ($1.fourth = $2.fourth) then 0 else 0 end +
            case when ($1.first != $2.first) then (
                    $1.first = $2.second or
                    $1.first = $2.third or
                    $1.first = $2.fourth
                    )::int else 0 end +
            case when ($1.second != $2.second) then (
                    $1.second = $2.first or
                    $1.second = $2.third or
                    $1.second = $2.fourth
                    )::int else 0 end +
            case when ($1.third != $2.third) then (
                    $1.third = $2.first or
                    $1.third = $2.second or
                    $1.third = $2.fourth
                    )::int else 0 end +
            case when ($1.fourth != $2.fourth) then (
                    $1.fourth = $2.first or
                    $1.fourth = $2.second or
                    $1.fourth = $2.third
                    )::int else 0 end
        ) from guesses
    $$ LANGUAGE SQL;



    SELECT guesses,
           check_black(guesses.*, mastermind.*),
           check_white(guesses.*, mastermind.*)
        FROM   guesses, mastermind

Wren

Translation of: Kotlin
Library: Wren-ioutil
Library: Wren-str
import "random" for Random
import "./ioutil" for Input
import "./str" for Str

var Rand = Random.new()

class Mastermind {
    construct new(codeLen, colorsCnt, guessCnt, repeatClr) {
        var color = "ABCDEFGHIJKLMNOPQRST"
        _codeLen = codeLen.clamp(4, 10)
        var cl = colorsCnt
        if (!repeatClr && cl < _codeLen) cl = _codeLen
        _colorsCnt = cl.clamp(2, 20)  
        _guessCnt = guessCnt.clamp(7, 20)
        _repeatClr = repeatClr
        _colors = color.take(_colorsCnt).join()
        _combo = ""
        _guesses = []
        _results = []
    }

    play() {
        var win = false
        _combo = getCombo_()
        while (_guessCnt != 0) {
            showBoard_()
            if (checkInput_(getInput_())) {
                win = true
                break
            }
            _guessCnt = _guessCnt - 1
        }
        System.print("\n\n--------------------------------")
        if (win) {
            System.print("Very well done!\nYou found the code: %(_combo)")
        } else {
            System.print("I am sorry, you couldn't make it!\nThe code was: %(_combo)")
        }
        System.print("--------------------------------\n")
    }

    showBoard_() {
        for (x in 0..._guesses.count) {
            System.print("\n--------------------------------")
            System.write("%(x + 1): ")
            for (y in _guesses[x]) System.write("%(y) ")
            System.write(" :  ")
            for (y in _results[x]) System.write("%(y) ")
            var z = _codeLen - _results[x].count
            if (z > 0) System.write("- " * z)
        }
        System.print("\n")
    }

    getInput_() {
        while (true) {
            var a = Str.upper(Input.text("Enter your guess (%(_colors)): ", 1)).take(_codeLen)
            if (a.all { |c| _colors.contains(c) } ) return a.join()
        }
    }

    checkInput_(a) {
        _guesses.add(a.toList)
        var black = 0
        var white = 0
        var gmatch = List.filled(_codeLen, false)
        var cmatch = List.filled(_codeLen, false)
        for (i in 0..._codeLen) {
            if (a[i] == _combo[i]) {
                gmatch[i] = true
                cmatch[i] = true
                black = black + 1
            }
        }
        for (i in 0..._codeLen) {
            if (gmatch[i]) continue
            for (j in 0..._codeLen) {
                if (i == j || cmatch[j]) continue
                if (a[i] == _combo[j]) {
                    cmatch[j] = true
                    white = white + 1
                    break
                }
            }
        }
        var r = []
        r.addAll(("X" * black).toList)
        r.addAll(("O" * white).toList)
        _results.add(r)
        return black == _codeLen
    }

    getCombo_() {
        var c =  ""
        var clr = _colors
        for (s in 0..._codeLen) {
            var z = Rand.int(clr.count)
            c = c + clr[z]
            if (!_repeatClr) Str.delete(clr, z)
        }
        return c
    }
}

var m = Mastermind.new(4, 8, 12, false)
m.play()
Output:

Sample game:

Enter your guess (ABCDEFGH): abcd

--------------------------------
1: A B C D  :  X - - - 

Enter your guess (ABCDEFGH): efgh

--------------------------------
1: A B C D  :  X - - - 
--------------------------------
2: E F G H  :  O O - - 

Enter your guess (ABCDEFGH): aefa

--------------------------------
1: A B C D  :  X - - - 
--------------------------------
2: E F G H  :  O O - - 
--------------------------------
3: A E F A  :  X X - - 

Enter your guess (ABCDEFGH): aagh

--------------------------------
1: A B C D  :  X - - - 
--------------------------------
2: E F G H  :  O O - - 
--------------------------------
3: A E F A  :  X X - - 
--------------------------------
4: A A G H  :  X O O O 

Enter your guess (ABCDEFGH): agah

--------------------------------
1: A B C D  :  X - - - 
--------------------------------
2: E F G H  :  O O - - 
--------------------------------
3: A E F A  :  X X - - 
--------------------------------
4: A A G H  :  X O O O 
--------------------------------
5: A G A H  :  X X O O 

Enter your guess (ABCDEFGH): agha


--------------------------------
Very well done!
You found the code: AGHA
--------------------------------

zkl

Translation of: C++
class MasterMind{
   fcn init(code_len,guess_count){
      var codeLen =code_len.max(4).min(10);
      var guessCnt=guess_count.max(7).min(20);
      var colors  ="ABCDEFGHIJKLMNOPQRST"[0,codeLen];
   }
   fcn play{
      guesses,win,blackWhite:=List(),False,Void;
      code:=codeLen.pump(String,'wrap(_){ colors[(0).random(codeLen)] });
      do(guessCnt){
	 str:=getInput();
	 win,blackWhite = checkInput(str,code);
	 guesses.append(T(str,blackWhite));
	 showBoard(guesses);
	 if(win) break;
      }
      if(win) println("--------------------------------\n",
		"Very well done!\nYou found the code: ",code);
       else println("--------------------------------\n",
		"I am sorry, you didn't discover the code!\nThe code was: ",code);
    }
    fcn [private] showBoard(guesses){
       foreach n,gbw in ([1..].zip(guesses)){
          guess,blackWhite := gbw;
          println("%2d: %s :% s %s".fmt(n,
	     guess.split("").concat(" "), blackWhite.split("").concat(" "),
	     "- "*(codeLen - blackWhite.len())));
       }
    }
    fcn [private] getInput{
       while(True){
	  a:=ask("Enter your guess (" + colors + "): ").toUpper()[0,codeLen];
	  if(not (a-colors) and a.len()>=codeLen) return(a);
       }
    }
    fcn [private] checkInput(guess,code){
	// black: guess is correct in both color and position
        // white: correct color, wrong position
	matched,black := guess.split("").zipWith('==,code), matched.sum(0);
	// remove black from code, prepend null to make counting easy
	code  = L("-").extend(matched.zipWith('wrap(m,peg){ m and "-" or peg },code));
	white:=0; foreach m,p in (matched.zip(guess)){
	   if(not m and (z:=code.find(p))){ white+=1; code[z]="-"; }
	}
	return(black==codeLen,"X"*black + "O"*white)
    }
}(4,12).play();
Output:
Enter your guess (ABCD): abcd
 1: A B C D : X O O - 
Enter your guess (ABCD): abcc
 1: A B C D : X O O - 
 2: A B C C : O O - - 
Enter your guess (ABCD): aaad
 1: A B C D : X O O - 
 2: A B C C : O O - - 
 3: A A A D : X - - - 
Enter your guess (ABCD): bccd
 1: A B C D : X O O - 
 2: A B C C : O O - - 
 3: A A A D : X - - - 
 4: B C C D : X X O - 
Enter your guess (ABCD): dcbd
 1: A B C D : X O O - 
 2: A B C C : O O - - 
 3: A A A D : X - - - 
 4: B C C D : X X O - 
 5: D C B D : X X X X 
--------------------------------
Very well done!
You found the code: DCBD