Generate random chess position
You are encouraged to solve this task according to the task description, using any language you may know.
- Task
Generate a random chess position in FEN format.
The position does not have to be realistic or even balanced, but it must comply to the following rules:
- there is one and only one king of each color (one black king and one white king);
- the kings must not be placed on adjacent squares;
- there can not be any pawn in the promotion square (no white pawn in the eighth rank, and no black pawn in the first rank);
- including the kings, up to 32 pieces of either color can be placed.
- There is no requirement for material balance between sides.
- The picking of pieces does not have to comply to a regular chess set --- there can be five knights, twenty rooks, whatever ... as long as the total number of pieces do not exceed thirty-two.
- it is white's turn.
- It's assumed that both sides have lost castling rights and that there is no possibility for en passant (the FEN should thus end in w - - 0 1).
No requirement is made regarding the probability distribution of your method, but your program should be able to span a reasonably representative sample of all possible positions. For instance, programs that would always generate positions with say five pieces on the board, or with kings on a corner, would not be considered truly random.
11l
<lang 11l>V board = [[‘ ’] * 8] * 8 V piece_list = [‘R’, ‘N’, ‘B’, ‘Q’, ‘P’]
F place_kings(&brd)
L
V (rank_white, file_white, rank_black, file_black) = (random:(0 .. 7), random:(0 .. 7), random:(0 .. 7), random:(0 .. 7))
V diff_list = [abs(rank_white - rank_black), abs(file_white - file_black)]
I sum(diff_list) > 2 | Set(diff_list) == Set([0, 2])
(brd[rank_white][file_white], brd[rank_black][file_black]) = (Char(‘K’), Char(‘k’))
L.break
F pawn_on_promotion_square(pc, pr)
I pc == ‘P’ & pr == 0
R 1B
E I pc == ‘p’ & pr == 7
R 1B
R 0B
F populate_board(&brd, wp, bp)
L(x) 2
Int piece_amount
[Char] pieces
I x == 0
piece_amount = wp
pieces = :piece_list
E
piece_amount = bp
pieces = :piece_list.map(s -> s.lowercase())
L piece_amount != 0
V (piece_rank, piece_file) = (random:(0 .. 7), random:(0 .. 7))
V piece = random:choice(pieces)
I brd[piece_rank][piece_file] == ‘ ’ & pawn_on_promotion_square(piece, piece_rank) == 0B
brd[piece_rank][piece_file] = piece
piece_amount--
F fen_from_board(brd)
V fen = ‘’
L(x) brd
V n = 0
L(y) x
I y == ‘ ’
n++
E
I n != 0
fen ‘’= String(n)
fen ‘’= y
n = 0
I n != 0
fen ‘’= String(n)
fen ‘’= I fen.count(‘/’) < 7 {‘/’} E ‘’
fen ‘’= " w - - 0 1\n"
R fen
V (piece_amount_white, piece_amount_black) = (random:(0 .. 15), random:(0 .. 15)) place_kings(&board) populate_board(&board, piece_amount_white, piece_amount_black) print(fen_from_board(board)) L(x) board
print(‘[’x.map(c -> ‘'’c‘'’).join(‘, ’)‘]’)</lang>
- Output:
8/8/p7/4n3/3K4/2BbN1k1/4Q3/4R3 w - - 0 1 [' ', ' ', ' ', ' ', ' ', ' ', ' ', ' '] [' ', ' ', ' ', ' ', ' ', ' ', ' ', ' '] ['p', ' ', ' ', ' ', ' ', ' ', ' ', ' '] [' ', ' ', ' ', ' ', 'n', ' ', ' ', ' '] [' ', ' ', ' ', 'K', ' ', ' ', ' ', ' '] [' ', ' ', 'B', 'b', 'N', ' ', 'k', ' '] [' ', ' ', ' ', ' ', 'Q', ' ', ' ', ' '] [' ', ' ', ' ', ' ', 'R', ' ', ' ', ' ']
Action!
<lang Action!>DEFINE BOARDSIZE="64" DEFINE EMPTY="'."
BYTE FUNC AbsDist(BYTE a,b)
IF a>b THEN RETURN (a-b) FI
RETURN (b-a)
BYTE FUNC GetPiece(BYTE ARRAY board BYTE x,y) RETURN (board(x+y*8))
PROC PutPiece(BYTE ARRAY board BYTE x,y,piece)
board(x+y*8)=piece
RETURN
PROC PrintBoard(BYTE ARRAY board)
BYTE i,j,c
FOR j=0 TO 7
DO
FOR i=0 TO 7
DO
c=GetPiece(board,i,j)
Put(c)
OD
PutE()
OD
RETURN
PROC Append(CHAR ARRAY s CHAR c)
s(0)==+1 s(s(0))=c
RETURN
PROC ExportToFen(BYTE ARRAY board CHAR ARRAY fen)
CHAR ARRAY s=" w - - 0 1" INT x,y BYTE count,p
fen(0)=0
FOR y=0 TO 7
DO
x=0
WHILE x<8
DO
count=0
WHILE x<8 AND GetPiece(board,x,y)=EMPTY
DO
x==+1 count==+1
OD
IF count>0 THEN
Append(fen,'0+count)
ELSE
p=GetPiece(board,x,y)
Append(fen,p)
x==+1
FI
OD
IF y<7 THEN
Append(fen,'/)
FI
OD
FOR x=1 TO s(0) DO Append(fen,s(x)) OD
RETURN
PROC PutKings(BYTE ARRAY board)
BYTE x1,y1,x2,y2
DO
x1=Rand(8) y1=Rand(8)
x2=Rand(8) y2=Rand(8)
IF AbsDist(x1,x2)>1 AND AbsDist(y1,y2)>1 THEN
PutPiece(board,x1,y1,'K)
PutPiece(board,x2,y2,'k)
RETURN
FI
OD
RETURN
PROC PutPieces(BYTE ARRAY board CHAR ARRAY pieces)
BYTE i,x,y,p
FOR i=1 TO pieces(0)
DO
p=pieces(i)
DO
x=Rand(8)
IF p='P OR p='p THEN
y=Rand(6)+1
ELSE
y=Rand(8)
FI
UNTIL GetPiece(board,x,y)=EMPTY
OD
PutPiece(board,x,y,p)
OD
RETURN
PROC Generate(BYTE ARRAY board CHAR ARRAY pieces)
SetBlock(board,BOARDSIZE,EMPTY) PutKings(board) PutPieces(board,pieces)
RETURN
PROC Test(CHAR ARRAY pieces)
BYTE ARRAY board(BOARDSIZE) CHAR ARRAY fen(256)
Generate(board,pieces) PrintBoard(board) ExportToFen(board,fen) PrintE(fen) PutE()
RETURN
PROC Main()
Test("PPPPPPPPBBNNQRRppppppppbbnnqrr")
Test("PPBNQRppbnqr")
RETURN</lang>
- Output:
Screenshot from Atari 8-bit computer
.Q...R.. nnp.P.Pq pPpP.B.k ...prNp. P.p.B.P. .K.pb.pP .P...NRb ..r..... 1Q3R2/nnp1P1Pq/pPpP1B1k/3prNp1/P1p1B1P1/1K1pb1pP/1P3NRb/2r5 w - - 0 1 ........ ....n.bp k...p... ...B.... r.PP.... q..K...R .....Q.N ........ 8/4n1bp/k3p3/3B4/r1PP4/q2K3R/5Q1N/8 w - - 0 1
C
<lang c>#include <stdio.h>
- include <math.h>
- include <string.h>
- include <stdlib.h>
- include <time.h>
- define TRUE 1
- define FALSE 0
typedef int bool;
char grid[8][8];
void placeKings() {
int r1, r2, c1, c2;
for (;;) {
r1 = rand() % 8;
c1 = rand() % 8;
r2 = rand() % 8;
c2 = rand() % 8;
if (r1 != r2 && abs(r1 - r2) > 1 && abs(c1 - c2) > 1) {
grid[r1][c1] = 'K';
grid[r2][c2] = 'k';
return;
}
}
}
void placePieces(const char *pieces, bool isPawn) {
int n, r, c;
int numToPlace = rand() % strlen(pieces);
for (n = 0; n < numToPlace; ++n) {
do {
r = rand() % 8;
c = rand() % 8;
}
while (grid[r][c] != 0 || (isPawn && (r == 7 || r == 0)));
grid[r][c] = pieces[n];
}
}
void toFen() {
char fen[80], ch;
int r, c, countEmpty = 0, index = 0;
for (r = 0; r < 8; ++r) {
for (c = 0; c < 8; ++c) {
ch = grid[r][c];
printf("%2c ", ch == 0 ? '.' : ch);
if (ch == 0) {
countEmpty++;
}
else {
if (countEmpty > 0) {
fen[index++] = countEmpty + 48;
countEmpty = 0;
}
fen[index++] = ch;
}
}
if (countEmpty > 0) {
fen[index++] = countEmpty + 48;
countEmpty = 0;
}
fen[index++]= '/';
printf("\n");
}
strcpy(fen + index, " w - - 0 1");
printf("%s\n", fen);
}
char *createFen() {
placeKings();
placePieces("PPPPPPPP", TRUE);
placePieces("pppppppp", TRUE);
placePieces("RNBQBNR", FALSE);
placePieces("rnbqbnr", FALSE);
toFen();
}
int main() {
srand(time(NULL)); createFen(); return 0;
}</lang>
- Output:
Sample position:
. . . Q . . b . . . . . . . . . R . . b . . r . . . . . q . . K . . . . P . . . . B k P . . . . . n . . . . . . . . . N . . . . 3Q2b1/8/R2b2r1/4q2K/4P3/1BkP4/1n6/3N4/ w - - 0 1
C++
<lang cpp>
- include <ctime>
- include <iostream>
- include <string>
- include <algorithm>
class chessBoard { public:
void generateRNDBoard( int brds ) {
int a, b, i; char c;
for( int cc = 0; cc < brds; cc++ ) {
memset( brd, 0, 64 );
std::string pieces = "PPPPPPPPNNBBRRQKppppppppnnbbrrqk";
random_shuffle( pieces.begin(), pieces.end() );
while( pieces.length() ) {
i = rand() % pieces.length(); c = pieces.at( i );
while( true ) {
a = rand() % 8; b = rand() % 8;
if( brd[a][b] == 0 ) {
if( c == 'P' && !b || c == 'p' && b == 7 ||
( ( c == 'K' || c == 'k' ) && search( c == 'k' ? 'K' : 'k', a, b ) ) ) continue;
break;
}
}
brd[a][b] = c;
pieces = pieces.substr( 0, i ) + pieces.substr( i + 1 );
}
print();
}
}
private:
bool search( char c, int a, int b ) {
for( int y = -1; y < 2; y++ ) {
for( int x = -1; x < 2; x++ ) {
if( !x && !y ) continue;
if( a + x > -1 && a + x < 8 && b + y >-1 && b + y < 8 ) {
if( brd[a + x][b + y] == c ) return true;
}
}
}
return false;
}
void print() {
int e = 0;
for( int y = 0; y < 8; y++ ) {
for( int x = 0; x < 8; x++ ) {
if( brd[x][y] == 0 ) e++;
else {
if( e > 0 ) { std::cout << e; e = 0; }
std::cout << brd[x][y];
}
}
if( e > 0 ) { std::cout << e; e = 0; }
if( y < 7 ) std::cout << "/";
}
std::cout << " w - - 0 1\n\n";
for( int y = 0; y < 8; y++ ) {
for( int x = 0; x < 8; x++ ) {
if( brd[x][y] == 0 ) std::cout << ".";
else std::cout << brd[x][y];
}
std::cout << "\n";
}
std::cout << "\n\n"; } char brd[8][8];
}; int main( int argc, char* argv[] ) {
srand( ( unsigned )time( 0 ) ); chessBoard c; c.generateRNDBoard( 2 ); return 0;
} </lang>
- Output:
1R6/2bnQP1K/br1N1BP1/nPkp1P2/2p1P1P1/4Ppqp/p1r1ppp1/1PNR3B w - - 0 1 .R...... ..bnQP.K br.N.BP. nPkp.P.. ..p.P.P. ....Ppqp p.r.ppp. .PNR...B 1n1k2bp/1PppQpb1/N1p4p/1B2P1K1/1RB2P2/pPR1Np2/P1r1rP1P/P2q3n w - - 0 1 .n.k..bp .PppQpb. N.p....p .B..P.K. .RB..P.. pPR.Np.. P.r.rP.P P..q...n
Crystal
<lang ruby>def hasNK(board, a, b)
(-1..1).each do |g|
(-1..1).each do |f|
aa = a + f; bb = b + g
if (0..7).includes?(aa) && (0..7).includes?(bb)
p = board[aa + 8 * bb]
return true if p == "K" || p == "k"
end
end
end
return false
end
def generateBoard(board, pieces)
pieces.each_char do |p|
while true
a = rand(8); b = rand(8)
next if ( (b == 0 || b == 7) && (p == "P" || p == "p") ) ||
( (p == "k" || p == "K") && hasNK(board, a, b) )
break if board[a + b * 8] == '.'
end
board[a + b * 8] = p
end
end
pieces = "ppppppppkqrrbbnnPPPPPPPPKQRRBBNN" 11.times do
e = pieces.size - 1
while e > 0
p = rand(e); t = pieces[e]
#pieces[e] = pieces[p]; pieces[p] = t; e -= 1 # in Ruby
pieces = pieces.sub(e, pieces[p]) # in Crystal because
pieces = pieces.sub(p, t); e -= 1 # strings immutable
end
end
- No 'nil' for Crystal arrays; use '.' for blank value
board = Array.new(64, '.'); generateBoard(board, pieces) puts e = 0 8.times do |j| row_j = j * 8
8.times do |i|
board[row_j + i ] == '.' ? (e += 1) :
( (print(e); e = 0) if e > 0
print board[row_j + i] )
end
(print(e); e = 0) if e > 0
print("/") if j < 7
end
print(" w - - 0 1\n") 8.times do |j| row_j = j * 8
8.times { |i| board[row_j + i] == '.' ? print(".") : print(board[row_j + i]) }
puts
end
- Simpler for same output
8.times{ |row| puts board[row*8..row*8 + 7].join("") }</lang>
- Output:
1n1P3p/1p1k2Pp/1ppPPprn/2rP4/KNRQ2b1/2Bp1PP1/3qPBN1/2Rp4 w - - 0 1.n.P...p .p.k..Pp .ppPPprn ..rP.... KNRQ..b. ..Bp.PP. ...qPBN. ..Rp....
Factor
<lang factor>USING: combinators.short-circuit grouping io kernel math math.parser math.ranges math.vectors prettyprint random sequences sets splitting.monotonic strings ; IN: rosetta-code.random-chess-position
<PRIVATE
CONSTANT: pieces "RNBQBNRPPPPPPPPrnbqbnrpppppppp" CONSTANT: empty CHAR: .
- <empty-board> ( -- seq ) 64 [ empty ] "" replicate-as ;
- empty-index ( seq -- n ) empty swap indices random ;
- place ( seq elt n -- seq' ) rot [ set-nth ] keep ;
! return a list of indices that are adjacent to n
- adj ( n -- seq )
[ 1 - ] [ 1 + ] bi [a,b] { 8 8 8 } [ v- ] 2keep dupd v+
append append ;
- rand-non-adjacent ( m -- n ) 64 <iota> swap adj diff random ;
- place-kings ( seq -- seq' )
CHAR: K over empty-index [ place ] keep [ CHAR: k ] dip rand-non-adjacent place ;
- non-pawn ( seq elt -- seq' ) over empty-index place ;
! prevent placing of pawns in ranks 1 and 8
- pawn ( seq elt -- seq' )
over empty swap indices
[ { [ 7 > ] [ 56 < ] } 1&& ] filter random place ;
- place-piece ( seq -- seq' )
pieces random dup "Pp" member? [ pawn ] [ non-pawn ] if ;
PRIVATE>
- position ( -- seq )
<empty-board> place-kings 30 random [ place-piece ] times ;
- position. ( seq -- )
[ 1string ] { } map-as 8 group simple-table. ;
- position>fen ( seq -- seq' )
8 group [
[ = ] monotonic-split
[ dup first empty = [ length number>string ] when ]
map concat
] map "/" join "/ w - - 0 1" append ;
- random-chess-position-demo ( -- )
position [ position. ] [ position>fen print ] bi ;
MAIN: random-chess-position-demo</lang>
- Output:
. . . . . . . . . p . . . . . . . . . Q R . . . . . . . . . k . . P . . b . . . . . P . . . K . . . . . . . b . . . . . . . r . 8/1p6/3QR3/6k1/1P2b3/2P3K1/6b1/6r1/ w - - 0 1
FreeBASIC
<lang freebasic> Dim Shared As Byte grid(8, 8), r, c
Sub placeKings()
Dim As Byte r1, r2, c1, c2
Do
r1 = Int(Rnd*8)
c1 = Int(Rnd*8)
r2 = Int(Rnd*8)
c2 = Int(Rnd*8)
If (r1 <> r2 And Abs(r1 - r2) > 1 And Abs(c1 - c2) > 1) Then
grid(r1, c1) = Asc("K")
grid(r2, c2) = Asc("k")
Return
End If
Loop
End Sub
Sub placePieces(pieces As String, isPawn As Byte)
Dim numToPlace As Byte = Int(Rnd*(Len(pieces)))
For n As Byte = 0 To numToPlace-1
Do
r = Int(Rnd*8)
c = Int(Rnd*8)
Loop Until(Not(grid(r, c) Or (isPawn And (r = 7 Or r = 0))))
grid(r, c) = Asc(Mid(pieces, n, 1))
Next n
End Sub
Sub toFen()
Dim As Byte ch, countEmpty = 0
Dim As String fen
For r = 0 To 8-1
For c = 0 To 8-1
ch = grid(r, c)
If ch <> 0 Then
Print " " & Chr(ch);
Else
Print " .";
End If
If ch = 0 Then
countEmpty += 1
Else
If countEmpty > 0 Then
fen += Chr(countEmpty + 48)
countEmpty = 0
End If
fen += Chr(ch)
End If
Next c
If countEmpty > 0 Then
fen += Chr(countEmpty + 48)
countEmpty = 0
End If
fen += "/"
Print
Next r
fen += " w - - 0 1"
Print fen
End Sub
Randomize Timer placeKings() placePieces("PPPPPPPP", True) placePieces("pppppppp", True) placePieces("RNBQBNR", False) placePieces("rnbqbnr", False) toFen() Sleep </lang>
- Output:
. . . . . . . . . . . . . . p . . . k P . . . . . . . . . b . . p . p . . p K . . Q . . p . r . . q . . . . . . . . . N . B n . 8/6p1/2kP4/5b2/p1p2pK1/1Q2p1r1/1q6/3N1Bn1/ w - - 0 1
FutureBasic
<lang futurebasic> include "NSLog.incl"
begin globals short grid(8, 8) // 1-8 end globals
local fn PlaceKings
'~'1
short r1, r2, c1, c2
while (YES) r1 = rnd(8) c1 = rnd(8) r2 = rnd(8) c2 = rnd(8) if ( r1 != r2 and abs( r1 - r2 ) > 1 and abs( c1 - c2) > 1 ) grid(r1, c1) = asc("K") grid(r2, c2) = asc("k") exit fn end if wend end fn
local fn PlacePieces( pieces$ as Str255, isPawn as BOOL )
'~'1
short n, r, c, numToPlace
numToPlace = rnd( len$(pieces$) ) for n = 1 to numToPlace do r = rnd(8) c = rnd(8) if isPawn == YES and mid$( pieces$, n, 1 ) == "p" and r = 8 then exit fn if isPawn == YES and mid$( pieces$, n, 1 ) == "P" and r = 1 then exit fn until not( ( grid(r, c) != 0 ) or ( isPawn and ( r == 8 or r == 1 ) ) ) grid(r, c) = asc( mid$( pieces$, n, 1 ) ) next end fn
local fn ToFen
'~'1
Str255 fen$
short ch, r, c, countEmpty = 0
CFStringRef pieceStr
for r = 1 to 8 for c = 1 to 8 ch = grid(r, c)
select (ch)
case 107 : pieceStr = @" ♚" // Black King case 75 : pieceStr = @" ♔" // White King
case 112 : pieceStr = @" ♟" // Black Pawn case 80 : pieceStr = @" ♙" // White Pawn
case 114 : pieceStr = @" ♜" // Black Rook case 82 : pieceStr = @" ♖" // White Rook
case 110 : pieceStr = @" ♞" // Black Knight case 78 : pieceStr = @" ♘" // White Knight
case 98 : pieceStr = @" ♝" // Black Bishop case 66 : pieceStr = @" ♗" // White Bishop
case 113 : pieceStr = @" ♛" // Black Queen case 81 : pieceStr = @" ♕" // White Queen
end select
if ( ch ) print pieceStr, else print @" .", end if if ( ch == 0 ) countEmpty++ else if ( countEmpty > 0 ) fen$ = fen$ + chr$(countEmpty + 48) countEmpty = 0 end if fen$ = fen$ + chr$(ch) end if next if ( countEmpty > 0 ) fen$ = fen$ + chr$(countEmpty + 48) countEmpty = 0 end if fen$ = fen$ + "/" print next fen$ = fen$ + " w - - 0 1" fen$ = mid$( fen$, 8, len$(fen$) ) print text @"Menlo", 14, fn ColorText, fn ColorClear, NSTextAlignmentLeft, 10 print fen$ end fn
local fn CreateFen fn PlaceKings fn PlacePieces( "PPPPPPPP", YES ) fn PlacePieces( "pppppppp", YES ) fn PlacePieces( "RNBQBNR", NO ) fn PlacePieces( "rnbqbnr", NO ) fn ToFen end fn
randomize
window 1, @"Random Chess Position", ( 0, 0, 700, 400 )
text @"Menlo", 32, fn ColorText, fn ColorClear, NSTextAlignmentLeft, 10
fn CreateFen
NSLogSetFont( fn FontWithName( @"Menlo", 24 ) ) NSLogSetTabInterval( 30 ) NSLog( @"%@", fn WindowPrintViewString( 1 ) )
HandleEvents
</lang>
Go
<lang go>package main
import (
"fmt" "math/rand" "strconv" "strings" "time"
)
var grid [8][8]byte
func abs(i int) int {
if i >= 0 {
return i
} else {
return -i
}
}
func createFen() string {
placeKings()
placePieces("PPPPPPPP", true)
placePieces("pppppppp", true)
placePieces("RNBQBNR", false)
placePieces("rnbqbnr", false)
return toFen()
}
func placeKings() {
for {
r1 := rand.Intn(8)
c1 := rand.Intn(8)
r2 := rand.Intn(8)
c2 := rand.Intn(8)
if r1 != r2 && abs(r1-r2) > 1 && abs(c1-c2) > 1 {
grid[r1][c1] = 'K'
grid[r2][c2] = 'k'
return
}
}
}
func placePieces(pieces string, isPawn bool) {
numToPlace := rand.Intn(len(pieces))
for n := 0; n < numToPlace; n++ {
var r, c int
for {
r = rand.Intn(8)
c = rand.Intn(8)
if grid[r][c] == '\000' && !(isPawn && (r == 7 || r == 0)) {
break
}
}
grid[r][c] = pieces[n]
}
}
func toFen() string {
var fen strings.Builder
countEmpty := 0
for r := 0; r < 8; r++ {
for c := 0; c < 8; c++ {
ch := grid[r][c]
if ch == '\000' {
ch = '.'
}
fmt.Printf("%2c ", ch)
if ch == '.' {
countEmpty++
} else {
if countEmpty > 0 {
fen.WriteString(strconv.Itoa(countEmpty))
countEmpty = 0
}
fen.WriteByte(ch)
}
}
if countEmpty > 0 {
fen.WriteString(strconv.Itoa(countEmpty))
countEmpty = 0
}
fen.WriteString("/")
fmt.Println()
}
fen.WriteString(" w - - 0 1")
return fen.String()
}
func main() {
rand.Seed(time.Now().UnixNano()) fmt.Println(createFen())
}</lang>
- Output:
Sample position:
. q . . . . . . . . . p . . . K . . . . . . . b . r . b . . . . . . . k . . . . . . . . . . p . . . . . . . . . . n n . . . . . 1q6/3p3K/7b/1r1b4/3k4/6p1/8/1nn5/ w - - 0 1
Haskell
Module RandomChess <lang haskell>{-# LANGUAGE LambdaCase, TupleSections #-}
module RandomChess ( placeKings , placePawns , placeRemaining , emptyBoard , toFen , ChessBoard , Square (..) , BoardState (..) , getBoard ) where
import Control.Monad.State (State, get, gets, put) import Data.List (find, sortBy) import System.Random (Random, RandomGen, StdGen, random, randomR)
type Pos = (Char, Int)
type ChessBoard = [(Square, Pos)]
data PieceRank = King | Queen | Rook | Bishop | Knight | Pawn
deriving (Enum, Bounded, Show, Eq, Ord)
data PieceColor = Black | White
deriving (Enum, Bounded, Show, Eq, Ord)
data Square = ChessPiece PieceRank PieceColor | EmptySquare
deriving (Eq, Ord)
type PieceCount = [(Square, Int)]
data BoardState = BoardState { board :: ChessBoard , generator :: StdGen }
instance Show Square where
show (ChessPiece King Black) = "♚" show (ChessPiece Queen Black) = "♛" show (ChessPiece Rook Black) = "♜" show (ChessPiece Bishop Black) = "♝" show (ChessPiece Knight Black) = "♞" show (ChessPiece Pawn Black) = "♟" show (ChessPiece King White) = "♔" show (ChessPiece Queen White) = "♕" show (ChessPiece Rook White) = "♖" show (ChessPiece Bishop White) = "♗" show (ChessPiece Knight White) = "♘" show (ChessPiece Pawn White) = "♙" show EmptySquare = " "
instance Random PieceRank where
randomR (a, b) g = case randomR (fromEnum a, fromEnum b) g of (x, g) -> (toEnum x, g) random = randomR (minBound, maxBound)
instance Random PieceColor where
randomR (a, b) g = case randomR (fromEnum a, fromEnum b) g of (x, g) -> (toEnum x, g) random = randomR (minBound, maxBound)
fullBoard :: PieceCount fullBoard =
[ (ChessPiece King Black , 1) , (ChessPiece Queen Black , 1) , (ChessPiece Rook Black , 2) , (ChessPiece Bishop Black, 2) , (ChessPiece Knight Black, 2) , (ChessPiece Pawn Black , 8) , (ChessPiece King White , 1) , (ChessPiece Queen White , 1) , (ChessPiece Rook White , 2) , (ChessPiece Bishop White, 2) , (ChessPiece Knight White, 2) , (ChessPiece Pawn White , 8) , (EmptySquare , 32) ]
emptyBoard :: ChessBoard emptyBoard = fmap (EmptySquare,) . (,) <$> ['a'..'h'] <*> [1..8]
replaceSquareByPos :: (Square, Pos) -> ChessBoard -> ChessBoard replaceSquareByPos e@(_, p) = fmap (\x -> if p == snd x then e else x)
isPosOccupied :: Pos -> ChessBoard -> Bool isPosOccupied p = occupied . find (\x -> p == snd x)
where occupied (Just (EmptySquare, _)) = False occupied _ = True
isAdjacent :: Pos -> Pos -> Bool isAdjacent (x1, y1) (x2, y2) =
let upOrDown = (pred y1 == y2 || succ y1 == y2)
leftOrRight = (pred x1 == x2 || succ x1 == x2)
in (x2 == x1 && upOrDown)
|| (pred x1 == x2 && upOrDown)
|| (succ x1 == x2 && upOrDown)
|| (leftOrRight && y1 == y2)
fen :: Square -> String fen (ChessPiece King Black) = "k" fen (ChessPiece Queen Black) = "q" fen (ChessPiece Rook Black) = "r" fen (ChessPiece Bishop Black) = "b" fen (ChessPiece Knight Black) = "n" fen (ChessPiece Pawn Black) = "p" fen (ChessPiece King White) = "K" fen (ChessPiece Queen White) = "Q" fen (ChessPiece Rook White) = "R" fen (ChessPiece Bishop White) = "B" fen (ChessPiece Knight White) = "N" fen (ChessPiece Pawn White) = "P"
boardSort :: (Square, Pos) -> (Square, Pos) -> Ordering boardSort (_, (x1, y1)) (_, (x2, y2)) | y1 < y2 = GT
| y1 > y2 = LT
| y1 == y2 = compare x1 x2
toFen :: ChessBoard -> String toFen [] = " w - - 0 1" <> [] toFen b = scanRow (fst <$> take 8 b) 0
where scanRow [] 0 = nextRow scanRow [] n = show n <> nextRow scanRow (EmptySquare:xs) n = scanRow xs (succ n) scanRow (x:xs) 0 = nextPiece x xs scanRow (x:xs) n = show n <> nextPiece x xs nextRow = "/" <> toFen (drop 8 b) nextPiece x xs = fen x <> scanRow xs 0
-- State functions withStateGen :: (StdGen -> (a, StdGen)) -> State BoardState a withStateGen f = do
currentState <- get
let gen1 = generator currentState
let (x, gen2) = f gen1
put (currentState {generator = gen2})
pure x
randomPos :: State BoardState Pos randomPos = do
boardState <- gets board
chr <- withStateGen (randomR ('a', 'h'))
num <- withStateGen (randomR (1, 8))
let pos = (chr, num)
if isPosOccupied pos boardState then
randomPos
else
pure pos
randomPiece :: State BoardState Square randomPiece = ChessPiece <$> withStateGen random <*> withStateGen random
placeKings :: State BoardState () placeKings = do
currentState <- get
p1 <- randomPos
p2 <- randomPos
if p1 `isAdjacent` p2 || p1 == p2
then placeKings
else do
let updatedBoard = replaceSquareByPos (ChessPiece King White, p1) $
replaceSquareByPos (ChessPiece King Black, p2) (board currentState)
put currentState { board = updatedBoard }
placePawns :: State BoardState () placePawns = withStateGen (randomR (1, 16)) >>= go
where
go :: Int -> State BoardState ()
go 0 = pure ()
go n = do
currentState <- get
pos <- randomPos
color <- withStateGen random
let pawn = ChessPiece Pawn color
let currentBoard = board currentState
if promoted color == snd pos || isPosOccupied pos currentBoard ||
enpassant color == snd pos || firstPos color == snd pos
then go n
else do
put currentState { board = replaceSquareByPos (pawn, pos) currentBoard }
go $ pred n
promoted White = 8
promoted Black = 1
enpassant White = 5
enpassant Black = 4
firstPos White = 1
firstPos Black = 8
placeRemaining :: State BoardState () placeRemaining =
withStateGen (randomR (5, sum $ fmap snd remaining)) >>= go remaining
where
remaining = filter (\case
(ChessPiece King _, _) -> False
(ChessPiece Pawn _, _) -> False
(EmptySquare, _) -> False
_ -> True)
fullBoard
go :: PieceCount -> Int -> State BoardState ()
go _ 0 = pure ()
go remaining n = do
currentState <- get
let currentBoard = board currentState
position <- randomPos
piece <- randomPiece
if not (isPermitted piece) || isPosOccupied position currentBoard
then go remaining n
else do
let updatedBoard = replaceSquareByPos (piece, position) currentBoard
put currentState { board = updatedBoard }
go (consume piece remaining) (pred n)
where
isPermitted p =
case find ((==p) . fst) remaining of
Just (_, count) -> count > 0
Nothing -> False
consume p = fmap (\(p, c) -> if p == p then (p, pred c) else (p, c))
getBoard :: State BoardState ChessBoard getBoard = gets (sortBy boardSort . board)</lang>
Module Main <lang haskell>module Main where
import Control.Monad.State (evalState) import RandomChess (ChessBoard, emptyBoard, placeKings, getBoard,
placePawns, placeRemaining, toFen, BoardState (..))
import System.Random (newStdGen)
draw :: ChessBoard -> IO () draw b = do
showXAxis >> drawLine
mapM_ (\b@(p, (x,y)) ->
case x of 'h' -> putStr (" | " <> show p <> " | " <> show y <> "\n") >> drawLine
'a' -> putStr (show y <> " | " <> show p)
_ -> putStr (" | " <> show p)
)
b
showXAxis >> putStrLn "" >> putStrLn (toFen b)
where
drawLine = putStrLn (" " <> replicate 33 '-')
showXAxis = do
putStr " "
mapM_ (\(_, (x, _)) -> putStr $ " " <> [x]) (take 8 b)
putStrLn ""
main :: IO () main = BoardState emptyBoard <$> newStdGen >>= draw . evalState buildBoard
where buildBoard = placeKings >> placePawns >> placeRemaining >> getBoard</lang>
- Output:
Run 1
a b c d e f g h
---------------------------------
8 | | | ♜ | ♘ | | | ♞ | | 8
---------------------------------
7 | ♙ | ♟ | ♟ | ♔ | ♙ | ♙ | | ♙ | 7
---------------------------------
6 | | | | ♛ | | | | | 6
---------------------------------
5 | ♘ | | | | | | | ♟ | 5
---------------------------------
4 | | | ♙ | | | ♗ | ♙ | | 4
---------------------------------
3 | ♟ | ♕ | ♜ | ♟ | | ♗ | ♚ | | 3
---------------------------------
2 | ♞ | | | | ♙ | | ♙ | ♟ | 2
---------------------------------
1 | | | ♖ | | | | | | 1
---------------------------------
a b c d e f g h
2rN2n1/PppKPP1P/3q4/N6p/2P2BP1/pQrp1Bk1/n3P1Pp/2R5/ w - - 0 1
Run 2
a b c d e f g h
---------------------------------
8 | | | | | ♚ | | | | 8
---------------------------------
7 | ♟ | ♔ | ♙ | | | | | | 7
---------------------------------
6 | ♟ | | ♜ | ♟ | | | | | 6
---------------------------------
5 | | | ♟ | | | | | | 5
---------------------------------
4 | | | | | | | | | 4
---------------------------------
3 | | ♟ | | | ♙ | | | ♛ | 3
---------------------------------
2 | | | | | ♟ | | | ♘ | 2
---------------------------------
1 | ♖ | ♖ | | | ♝ | | | | 1
---------------------------------
a b c d e f g h
4k3/pKP5/p1rp4/2p5/8/1p2P2q/4p2N/RR2b3/ w - - 0 1
etc...
J
Implementation:
<lang J>getlayout=:3 :0
whilst. NB. first two positions are non-adjacent kings
(0{pos) e. (1{pos)+(,-)1 7 8 9
do.
pos=: y?64
end.
)
randboard=:3 :0
n=: ?30 NB. number of non-king pieces on board
layout=: getlayout 2+n NB. where they go
white=: 0 1,?n#2 NB. which ones are white?
pawns=: 0 0,?n#2 NB. where are the pawns?
pawns=: pawns * 1- white*layout e.56+i.8
pawns=: pawns * 1-(1-white)*layout e.i.8
ptyp=: 'pkqbjnPKQBJN'{~(6*white)+1 1,(1-2}.pawns)*2+?n#4
8 8$ptyp layout}64#'.'
)
NB. fen compress a line fen1=:3 :0
for_n.8-i.8 do. y=. y rplc (#&'.';":) n end.
)
NB. translate 8x8 board to fen notation NB. (just the task specific crippled fen) b2fen=:3 :0
(}.;|.<@(('/',fen1)"1) y),' w - - 0 1'
)
randfen=:b2fen@randboard</lang>
Example use:
<lang J> randfen q6J/1pb1p1p1/1Jq2k2/4p1Pp/1pP5/1K2Bp2/5p2/1P4P1 w - - 0 1
randfen
1Q3Q2/1Kn5/1PP5/2P5/2kNq1J1/7J/1P6/8 w - - 0 1
randfen
8/8/7K/8/8/8/k7/8 w - - 0 1
randfen
p4n2/1Q6/8/8/8/p4k1K/8/P5Qn w - - 0 1
randfen
bk1q3J/8/1N4K1/N3P3/3BQ3/j1P3P1/7P/5jq1 w - - 0 1
randfen
b1Q1Bb1J/j1N1PpK1/PpB1P1Pp/2pp2PN/3nnk2/3J4/P6P/1N2Qb1J w - - 0 1 </lang>
Java
<lang java>import static java.lang.Math.abs; import java.util.Random;
public class Fen {
static Random rand = new Random();
public static void main(String[] args) {
System.out.println(createFen());
}
static String createFen() {
char[][] grid = new char[8][8];
placeKings(grid);
placePieces(grid, "PPPPPPPP", true);
placePieces(grid, "pppppppp", true);
placePieces(grid, "RNBQBNR", false);
placePieces(grid, "rnbqbnr", false);
return toFen(grid); }
static void placeKings(char[][] grid) {
int r1, c1, r2, c2;
while (true) {
r1 = rand.nextInt(8);
c1 = rand.nextInt(8);
r2 = rand.nextInt(8);
c2 = rand.nextInt(8);
if (r1 != r2 && abs(r1 - r2) > 1 && abs(c1 - c2) > 1)
break;
}
grid[r1][c1] = 'K';
grid[r2][c2] = 'k';
}
static void placePieces(char[][] grid, String pieces, boolean isPawn) {
int numToPlace = rand.nextInt(pieces.length());
for (int n = 0; n < numToPlace; n++) {
int r, c;
do {
r = rand.nextInt(8);
c = rand.nextInt(8);
} while (grid[r][c] != 0 || (isPawn && (r == 7 || r == 0)));
grid[r][c] = pieces.charAt(n);
}
}
static String toFen(char[][] grid) {
StringBuilder fen = new StringBuilder();
int countEmpty = 0;
for (int r = 0; r < 8; r++) {
for (int c = 0; c < 8; c++) {
char ch = grid[r][c];
System.out.printf("%2c ", ch == 0 ? '.' : ch);
if (ch == 0) {
countEmpty++;
} else {
if (countEmpty > 0) {
fen.append(countEmpty);
countEmpty = 0;
}
fen.append(ch);
}
}
if (countEmpty > 0) {
fen.append(countEmpty);
countEmpty = 0;
}
fen.append("/");
System.out.println();
}
return fen.append(" w - - 0 1").toString();
}
}</lang>
(lol, the black king is in check, it couldn't possibly be white's turn) . . . . . B . . P . P . . . . . . . k . R . . . p . P p . . . . . . . . . . . Q P . . . . . . . . N . . r N P . . . . . . . B K 5B2/P1P5/2k1R3/p1Pp4/7Q/P7/1N2rNP1/6BK/ w - - 0 1
JavaScript
<lang javascript> Array.prototype.shuffle = function() {
for (let i = this.length - 1; i > 0; i--) {
let j = Math.floor(Math.random() * (i + 1));
[this[i], this[j]] = [this[j], this[i]];
}
}
function randomFEN() {
let board = [];
for (let x = 0; x < 8; x++) board.push('. . . . . . . .'.split(' '));
function getRandPos() {
return [Math.floor(Math.random() * 8), Math.floor(Math.random() * 8)];
}
function isOccupied(pos) {
return board[pos[0]][pos[1]] != '.';
}
function isAdjacent(pos1, pos2) {
if (pos1[0] == pos2[0] || pos1[0] == pos2[0]-1 || pos1[0] == pos2[0]+1)
if (pos1[1] == pos2[1] || pos1[1] == pos2[1]-1 || pos1[1] == pos2[1]+1)
return true;
return false;
}
// place kings
let wk, bk;
do { wk = getRandPos(); bk = getRandPos(); }
while (isAdjacent(wk, bk));
board[wk[0]][wk[1]] = 'K';
board[bk[0]][bk[1]] = 'k';
// get peaces
let peaces = [];
let names = 'PRNBQ';
function pick() {
for (x = 1; x < Math.floor(Math.random() * 32); x++)
peaces.push(names[Math.floor(Math.random() * names.length)]);
}
pick();
names = names.toLowerCase();
pick();
peaces.shuffle();
// place peaces
while (peaces.length > 0) {
let p = peaces.shift(), pos;
// paws: cannot be placed in bottom or top row
if (p == 'p' || p == 'P')
do { pos = getRandPos() }
while (isOccupied(pos) || pos[0] == 0 || pos[0] == 7);
// everything else
else do { pos = getRandPos(); } while (isOccupied(pos));
board[pos[0]][pos[1]] = p;
}
// write FEN
let fen = [];
for (x = 0; x < board.length; x++) {
let str =, buf = 0;
for (let y = 0; y < board[x].length; y++)
if (board[x][y] == '.') buf++;
else {
if (buf > 0) { str += buf; buf = 0; }
str += board[x][y];
}
if (buf > 0) str += buf;
fen.push(str);
}
fen = fen.join('/') + ' w - - 0 1';
console.table(board); // for demonstrating purpose
return fen;
}
// example console.log(randomFEN()); </lang>
- Output:
X 0 1 2 3 4 5 6 7 0 . . . . Q . . . 1 . . . . Q . . . 2 . . . p . . . . 3 . . . . . . . R 4 . r r R . . . . 5 . . P . . . . . 6 . . . . . k . . 7 . . R . . . . K 4Q3/4Q3/3p4/7R/1rrR4/2P5/5k2/2R4K w - - 0 1
Julia
Module: <lang julia>module Chess
using Printf
struct King end struct Pawn end
function placepieces!(grid, ::King)
axis = axes(grid, 1)
while true
r1, c1, r2, c2 = rand(axis, 4)
if r1 != r2 && abs(r1 - r2) > 1 && abs(c1 - c2) > 1
grid[r1, c1] = '♚'
grid[r2, c2] = '♔'
return grid
end
end
end
function placepieces!(grid, ch)
axis = axes(grid, 1)
while true
r, c = rand(axis, 2)
if grid[r, c] == ' '
grid[r, c] = ch
return grid
end
end
end
function placepieces!(grid, ch, ::Pawn)
axis = axes(grid, 1)
while true
r, c = rand(axis, 2)
if grid[r, c] == ' ' && r ∉ extrema(axis)
grid[r, c] = ch
return grid
end
end
end
function randposition!(grid)
placepieces!(grid, King())
foreach("♙♙♙♙♙♙♙♙♙♟♟♟♟♟♟♟♟") do ch
placepieces!(grid, ch, Pawn())
end
foreach("♖♘♗♕♗♘♖♜♞♝♛♝♞♜") do ch
placepieces!(grid, ch)
end
return grid
end
printgrid(grid) = println(join((join(grid[r, :], ' ') for r in 1:size(grid, 1)), '\n'))
end # module Chess</lang>
Main: <lang julia>grid = fill(' ', 8, 8) Chess.randposition!(grid) Chess.printgrid(grid)</lang>
- Output:
♕ ♞ ♗
♖ ♙ ♔ ♙ ♖ ♜ ♙
♟ ♙ ♙ ♜
♘ ♝ ♙ ♙ ♟
♙ ♚ ♝ ♟
♟ ♟ ♗ ♟
♙ ♞ ♟ ♟
♘ ♛
Kotlin
<lang scala>// version 1.2.0
import java.util.Random import kotlin.math.abs
val rand = Random()
val grid = List(8) { CharArray(8) }
const val NUL = '\u0000'
fun createFen(): String {
placeKings()
placePieces("PPPPPPPP", true)
placePieces("pppppppp", true)
placePieces("RNBQBNR", false)
placePieces("rnbqbnr", false)
return toFen()
}
fun placeKings() {
while (true) {
val r1 = rand.nextInt(8)
val c1 = rand.nextInt(8)
val r2 = rand.nextInt(8)
val c2 = rand.nextInt(8)
if (r1 != r2 && abs(r1 - r2) > 1 && abs(c1 - c2) > 1) {
grid[r1][c1] = 'K'
grid[r2][c2] = 'k'
return
}
}
}
fun placePieces(pieces: String, isPawn: Boolean) {
val numToPlace = rand.nextInt(pieces.length)
for (n in 0 until numToPlace) {
var r: Int
var c: Int
do {
r = rand.nextInt(8)
c = rand.nextInt(8)
}
while (grid[r][c] != NUL || (isPawn && (r == 7 || r == 0)))
grid[r][c] = pieces[n]
}
}
fun toFen(): String {
val fen = StringBuilder()
var countEmpty = 0
for (r in 0..7) {
for (c in 0..7) {
val ch = grid[r][c]
print ("%2c ".format(if (ch == NUL) '.' else ch))
if (ch == NUL) {
countEmpty++
}
else {
if (countEmpty > 0) {
fen.append(countEmpty)
countEmpty = 0
}
fen.append(ch)
}
}
if (countEmpty > 0) {
fen.append(countEmpty)
countEmpty = 0
}
fen.append("/")
println()
}
return fen.append(" w - - 0 1").toString()
}
fun main(args: Array<String>) {
println(createFen())
}</lang>
Sample output:
. . . . . . . . K . . . . . . . . P p . b . P P . p P . . . P . . p . q . p P P . . . k . . . b . . . n p . . . . . r . . . . . 8/K7/1Pp1b1PP/1pP3P1/1p1q1pPP/3k3b/3np3/2r5/ w - - 0 1
Mathematica/Wolfram Language
<lang Mathematica>g = ConstantArray["", {8, 8}]; While[Norm@First@Differences[r = RandomChoice[Tuples[Range[8], 2], 2]] <= Sqrt[2], Null]; g = ReplacePart[g, {r1 -> "K", r2 -> "k"}]; avail = Position[g, "", {2}]; n = RandomInteger[{2, 14}]; rls = Thread[RandomSample[avail, n] -> RandomChoice[Characters@"NBRQnbrq", n]]; g = ReplacePart[g, rls]; avail = RandomSample[DeleteCases[Position[g, "", {2}], {8, _}], RandomInteger[{2, 8}]]; g = ReplacePart[g, Thread[avail -> "P"]]; avail = RandomSample[DeleteCases[Position[g, "", {2}], {1, _}], RandomInteger[{2, 8}]]; g = ReplacePart[g, Thread[avail -> "p"]]; g //= Map[Split]; g = g /. (x : {"" ..}) :> ToString[Length[x]]; g //= Map[StringJoin@*Flatten]; g = StringRiffle[Reverse[g], "/"]; g = g <> " w - - 0 1"; g</lang>
- Output:
2N5/1P3P2/p1P3P1/5q2/8/5k1K/1p3p2/8 w - - 0 1
Nim
<lang Nim>import random
type
Piece {.pure.} = enum
None
WhiteBishop = ('B', "♗")
WhiteKing = ('K', "♔")
WhiteKnight = ('N', "♘")
WhitePawn = ('P', "♙")
WhiteQueen = ('Q', "♕")
WhiteRook = ('R', "♖")
BlackBishop = ('b', "♝")
BlackKing = ('k', "♚")
BlackKnight = ('n', "♞")
BlackPawn = ('p', "♟")
BlackQueen = ('q', "♛")
BlackRook = ('r', "♜")
Color {.pure.} = enum White, Black
Grid = array[8, array[8, Piece]]
const
# White pieces except king and pawns.
WhitePieces = [WhiteQueen, WhiteRook, WhiteRook, WhiteBishop,
WhiteBishop, WhiteKnight, WhiteKnight]
# Black pieces except king and pawns.
BlackPieces = [BlackQueen, BlackRook, BlackRook, BlackBishop,
BlackBishop, BlackKnight, BlackKnight]
proc placeKings(grid: var Grid) =
while true:
let r1 = rand(7)
let c1 = rand(7)
let r2 = rand(7)
let c2 = rand(7)
if r1 != r2 and abs(r1 - r2) > 1 and abs(c1 - c2) > 1:
grid[r1][c1] = WhiteKing
grid[r2][c2] = BlackKing
break
proc placePawns(grid: var Grid; color: Color) =
let piece = if color == White: WhitePawn else: BlackPawn
let numToPlace = rand(8)
for n in 0..<numToPlace:
var r, c: int
while true:
r = rand(7)
c = rand(7)
if grid[r][c] == None and r notin {0, 7}: break
grid[r][c] = piece
proc placePieces(grid: var Grid; color: Color) =
var pieces = if color == White: WhitePieces else: BlackPieces
pieces.shuffle()
let numToPlace = rand(7)
for n in 0..<numToPlace:
var r, c: int
while true:
r = rand(7)
c = rand(7)
if grid[r][c] == None: break
grid[r][c] = pieces[n]
proc toFen(grid: Grid): string =
var countEmpty = 0
for r in 0..7:
for c in 0..7:
let piece = grid[r][c]
if piece == None:
stdout.write " . "
inc countEmpty
else:
stdout.write ' ' & $piece & ' '
if countEmpty > 0:
result.add $countEmpty
countEmpty = 0
result.add chr(ord(piece))
if countEmpty > 0:
result.add $countEmpty
countEmpty = 0
result.add '/' echo ""
result.add " w - - 0 1"
proc createFen(): string =
var grid: Grid grid.placeKings() grid.placePawns(White) grid.placePawns(Black) grid.placePieces(White) grid.placePieces(Black) result = grid.toFen()
randomize()
echo createFen()</lang>
- Output:
. . . . . . . . . . . . ♟ . . . ♟ . . . ♟ . . . . . . . . ♙ ♟ . . ♙ . . . ♚ . . . ♙ . . . . ♗ ♘ . ♟ . . ♙ . . . . . . ♔ . . . .
Perl
<lang perl>use strict; use warnings; use feature 'say'; use utf8; use List::AllUtils <shuffle any natatime>;
sub pick1 { return @_[rand @_] }
sub gen_FEN {
my $n = 1 + int rand 31; my @n = (shuffle(0 .. 63))[1 .. $n];
my @kings;
KINGS: {
for my $a (@n) {
for my $b (@n) {
next unless $a != $b && abs(int($a/8) - int($b/8)) > 1 || abs($a%8 - $b%8) > 1;
@kings = ($a, $b);
last KINGS;
}
die 'No good place for kings!';
}
}
my ($row, @pp);
my @pieces =
; my @k = rand() < .5 ? <K k> : <k K>; for my $sq (0 .. 63) { if (any { $_ == $sq } @kings) { push @pp, shift @k; } elsif (any { $_ == $sq } @n) { $row = 7 - int $sq / 8; push @pp, $row == 0 ? pick1(grep { $_ ne 'P' } @pieces) : $row == 7 ? pick1(grep { $_ ne 'P' } @pieces) : pick1(@pieces); } else { push @pp, 'ø'; } } my @qq; my $iter = natatime 8, @pp; while (my $row = join , $iter->()) { $row =~ s/((ø)\2*)/length($1)/eg; push @qq, $row; } return join('/', @qq) . ' w - - 0 1'; } say gen_FEN();</lang>
- Output:
p5Nq/1nn5/3N2bp/PRBkQr2/1QB1Pn2/Q5pK/1NRb2rN/p1R2r1N w - - 0 1
Phix
with javascript_semantics constant show_bad_boards = false string board function fen() string res = "" for i=1 to 64 by 8 do integer empty = 0 for j=i to i+7 do if board[j]='.' then empty += 1 else if empty then res &= empty+'0' empty = 0 end if res &= board[j] end if end for if empty then res &= empty+'0' end if if i<57 then res &= '/' end if end for res &= " w - - 0 1" return res end function function p15() string res = "pppppppprrnnbbq" -- promote 0..8 pawns for i=1 to rand(9)-1 do res[i] = res[rand(7)+8] end for res = shuffle(res) return res end function function kings_adjacent(sequence p12) integer {p1,p2} = sq_sub(p12,1), row_diff = abs(floor(p1/8)-floor(p2/8)), col_diff = abs(mod(p1,8)-mod(p2,8)) return row_diff<=1 and col_diff<=1 end function integer lp procedure show_board() printf(1,"%d pieces\n%s",{lp,join_by(board,1,8,"")}) end procedure while true do string pieces = "Kk"& -- kings upper(p15())[1..rand(16)-1]& -- white lower(p15())[1..rand(16)-1] -- black lp = length(pieces) sequence p = tagset(64) p = shuffle(p) board = repeat('.',64) for i=1 to lp do board[p[i]] = pieces[i] end for if kings_adjacent(p[1..2]) then if show_bad_boards then show_board() end if puts(1,"kings adjacent - reshuffle\n\n") else -- check no pawn will be on a promotion square, -- and (above spec) no pawn has gone backwards: if find('p',lower(board[1..8]&board[57..64]))=0 then exit end if if show_bad_boards then show_board() end if puts(1,"pawn on rank 1/8 - reshuffle\n\n") end if end while show_board() printf(1,"\n%s\n",{fen()})
To allow pawns that have "moved backwards", replace the inner test with
if not find('P',board[1..8]) and not find('p',board[57..64]) then exit end if
- Output:
with show_bad_boards set to true
28 pieces nR..rprR kp....Rp BQ..B.B. b..B...b .Kq.B.b. ....r.n. ppN..r.. .P...... pawn on rank 1/8 - reshuffle 28 pieces pnp...K. .q.....k b.P....p P..P..bp pPN.P.P. .BP..rRN QR....bN ....n... kings adjacent - reshuffle 10 pieces ......K. b......q ...nn... .....k.. ........ ..Q..n.. ..b..r.. ........ 6K1/b6q/3nn3/5k2/8/2Q2n2/2b2r2/8 w - - 0 1
PicoLisp
<lang PicoLisp>(load "@lib/simul.l") (seed (in "/dev/urandom" (rd 8))) (de pieceN (P)
(case P
("p" 8)
("q" 1)
(T 2) ) )
(de pieceset ()
(let C 0
(make
(for P (conc (cons "p") (shuffle '("r" "n" "b" "q")))
(let (X (pieceN P) N (rand 0 (+ X C)))
(do N
(link P) )
(if (= P "p")
(and
(> X N)
(inc 'C (- X N)) )
(and
(> N X)
(dec 'C (- N X)) ) ) ) ) ) ) )
(de neib (A)
(let
(X (/ (dec A) 8)
Y (% (dec A) 8) )
(filter
'((N)
(and
(<= 1 N 64)
(<=
(abs (- (/ (dec N) 8) X))
1 )
(<=
(abs (- (% (dec N) 8) Y))
1 ) ) )
(mapcar
'((B) (+ B A))
(-9 -8 -7 -1 1 7 8 9) ) ) ) )
(setq *B (need 64 ".")) (setq *P (conc (pieceset) (mapcar uppc (pieceset)) (cons "K"))) (for P *P
(loop
(T
(=
"."
(car
(setq @@
(nth
*B
(apply
rand
(if (or (= "p" P) (= "P" P))
(9 56)
(1 64) ) ) ) ) ) )
(set @@ P) ) ) )
(loop
(T
(and
(=
"."
(car
(setq @@ (nth *B (setq @@@ (rand 1 64)))) ) )
(fully
'((N) (<> "K" (get *B N)))
(neib @@@) ) )
(set @@ "k") ) )
(setq *FEN
(make
(while *B
(let (C 0 Lst (cut 8 '*B))
(prinl Lst)
(link
(make
(for L Lst
(if (= L ".")
(inc 'C)
(and
(gt0 C)
(link (swap 'C 0)) )
(link L) ) )
(and
(gt0 C)
(link C) ) ) ) ) ) ) )
(println (pack (glue "/" *FEN) " w - - 0 1"))</lang>
- Output:
...n...B .p.BQ.B. B..P..Br p......p r.PpBrrk ...B.P.. ...r..K. ......r. "3n3B/1p1BQ1B1/B2P2Br/p6p/r1PpBrrk/3B1P2/3r2K1/6r1 w - - 0 1"
Python
<lang python> import random
board = [[" " for x in range(8)] for y in range(8)] piece_list = ["R", "N", "B", "Q", "P"]
def place_kings(brd):
while True:
rank_white, file_white, rank_black, file_black = random.randint(0,7), random.randint(0,7), random.randint(0,7), random.randint(0,7)
diff_list = [abs(rank_white - rank_black), abs(file_white - file_black)]
if sum(diff_list) > 2 or set(diff_list) == set([0, 2]):
brd[rank_white][file_white], brd[rank_black][file_black] = "K", "k"
break
def populate_board(brd, wp, bp): for x in range(2): if x == 0: piece_amount = wp pieces = piece_list else: piece_amount = bp pieces = [s.lower() for s in piece_list] while piece_amount != 0: piece_rank, piece_file = random.randint(0, 7), random.randint(0, 7) piece = random.choice(pieces) if brd[piece_rank][piece_file] == " " and pawn_on_promotion_square(piece, piece_rank) == False: brd[piece_rank][piece_file] = piece piece_amount -= 1
def fen_from_board(brd): fen = "" for x in brd: n = 0 for y in x: if y == " ": n += 1 else: if n != 0: fen += str(n) fen += y n = 0 if n != 0: fen += str(n) fen += "/" if fen.count("/") < 7 else "" fen += " w - - 0 1\n" return fen
def pawn_on_promotion_square(pc, pr): if pc == "P" and pr == 0: return True elif pc == "p" and pr == 7: return True return False
def start():
piece_amount_white, piece_amount_black = random.randint(0, 15), random.randint(0, 15)
place_kings(board)
populate_board(board, piece_amount_white, piece_amount_black)
print(fen_from_board(board))
for x in board:
print(x)
- entry point
start() </lang>
- Output:
1p5k/1B4P1/1KN4R/nR3Nrb/Q1NrnpP1/7R/3PP3/1P5P w - - 0 1
[' ', 'p', ' ', ' ', ' ', ' ', ' ', 'k'] [' ', 'B', ' ', ' ', ' ', ' ', 'P', ' '] [' ', 'K', 'N', ' ', ' ', ' ', ' ', 'R'] ['n', 'R', ' ', ' ', ' ', 'N', 'r', 'b'] ['Q', ' ', 'N', 'r', 'n', 'p', 'P', ' '] [' ', ' ', ' ', ' ', ' ', ' ', ' ', 'R'] [' ', ' ', ' ', 'P', 'P', ' ', ' ', ' '] [' ', 'P', ' ', ' ', ' ', ' ', ' ', 'P']
R
<lang rsplus> place_kings <- function(brd){
###
# Function that puts the two kings on the board
# and makes sure that they are not adjacent
###
while (TRUE) {
# generate positions for white and black kings
rank_white <- sample(1:8, 1) ; file_white <- sample(1:8, 1)
rank_black <- sample(1:8, 1) ; file_black <- sample(1:8, 1)
# compute the differences between ranks and files
diff_vec <- c(abs(rank_white - rank_black), abs(file_white - file_black))
# if the two kings are not adjacent, place them on the board
if (sum(diff_vec) > 2 | setequal(diff_vec, c(0,2))) {
brd[rank_white, file_white] <- "K"
brd[rank_black, file_black] <- "k"
break
}
}
return(brd)
}
pawn_on_extreme_ranks <- function(pc, pr){
###
# Function that checks whether a pawn is on the first or eight rank
# (such a situation is not possible in chess)
###
if (pc %in% c("P","p") & pr %in% c(1,8))
return(TRUE)
else
return(FALSE)
}
populate_board <- function(brd, wp, bp){
###
# Function that puts pieces on the board making sure that they
# are not on the same squares, and verifying for pawn_on_extreme_ranks
###
# initialization
piece_list <- c("P", "N", "B", "R", "Q")
for (color in c("white", "black")){
# iterate for white (first) and black (after) pieces
if (color == "white"){
n_pieces = wp
pieces = piece_list
}
else {
n_pieces = bp
pieces = tolower(piece_list)
}
# place pieces one by one until we have them
while (n_pieces != 0){
piece_rank <- sample(1:8, 1) ; piece_file <- sample(1:8, 1)
piece <- sample(pieces, 1)
# check if square is empty and it is not a pawn on an extreme rank
if (brd[piece_rank, piece_file] == " " & !pawn_on_extreme_ranks(piece, piece_rank)){
brd[piece_rank, piece_file] <- piece
n_pieces <- n_pieces - 1
}
}
}
return(brd)
}
fen_from_board <- function(brd){
###
# Function that prints out the FEN of a given input board
###
# create vector of positions by row
fen <- apply(brd, 1, function(x) {
r <- rle(x)
paste(ifelse(r$values == " ", r$lengths, r$values), collapse = "")
})
# paste them together with separator '/' and add the final string
fen <- paste(paste(fen, collapse = "/"), "w - - 0 1")
return(fen)
}
generate_fen <- function(){
###
# This function calls all the functions above and generates
# the board representation along with its FEN
###
# initialization
board <- matrix(" ", nrow = 8, ncol = 8)
# generate random amount of white and black pieces (kings excluded)
n_pieces_white <- sample(0:31, 1) ; n_pieces_black <- sample(0:31, 1)
# place kings on board
board <- place_kings(board)
# put other pieces on board
board <- populate_board(board, wp = n_pieces_white, bp = n_pieces_black)
# print board and FEN
print(board)
cat("\n")
cat(fen_from_board(board))
}
generate_fen() </lang>
- Output:
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [1,] " " " " "n" " " " " "r" " " " " [2,] " " " " " " " " " " "B" " " " " [3,] " " " " " " " " "k" "p" " " " " [4,] " " "r" " " "q" " " " " "b" " " [5,] " " " " " " "r" "n" " " "r" " " [6,] " " " " " " "Q" "b" "r" " " "K" [7,] " " "n" " " " " " " "b" "p" " " [8,] " " " " " " " " " " " " " " " "
2n2r2/5B2/4kp2/1r1q2b1/3rn1r1/3Qbr1K/1n3bp1/8 w - - 0 1
Raku
(formerly Perl 6) <lang perl6>sub pick-FEN {
# First we chose how many pieces to place my $n = (2..32).pick;
# Then we pick $n squares my @n = (^64).pick($n);
# We try to find suitable king positions on non-adjacent squares.
# If we could not find any, we return recursively
return pick-FEN() unless
my @kings[2] = first -> [$a, $b] {
$a !== $b && abs($a div 8 - $b div 8) | abs($a mod 8 - $b mod 8) > 1
}, (@n X @n);
# We make a list of pieces we can pick (apart from the kings)
my @pieces =
; # We make a list of two king symbols to pick randomly a black or white king my @k = <K k>.pick(*); return (gather for ^64 -> $sq { if $sq == @kings.any { take @k.shift } elsif $sq == @n.any { my $row = 7 - $sq div 8; take $row == 7 ?? @pieces.grep(none('P')).pick !! $row == 0 ?? @pieces.grep(none('p')).pick !! @pieces.pick; } else { take 'ø' } }).rotor(8)».join».subst(/ø+/,{ .chars }, :g).join('/') ~ ' w - - 0 1'; } say pick-FEN();</lang>
- Output:
q2n1n2/1Qpk3Q/1r3bP1/1b1b4/2pRBR2/4P1bN/2R3K1/N1r2rPB w - - 0 1
REXX
This REXX version normally generates balanced number of pieces (both sides have an equal number of total pieces,
but not necessarily of the same kind).
If the number of chessboards specified is negative, then the number of chess pieces for each side will be random.
This version also allows any number of chessboards to be displayed (the default is to only display one chessboard). <lang rexx>/*REXX program generates a chess position (random pieces & positions) in a FEN format.*/ parse arg seed CBs . /*obtain optional arguments from the CL*/ if datatype(seed,'W') then call random ,,seed /*SEED given for RANDOM repeatability? */ if CBs== | CBs=="," then CBs=1 /*CBs: number of generated ChessBoards*/
/* [↓] maybe display any # of boards. */
do boards=1 for abs(CBs) /* [↓] maybe display separator & title*/
if sign(CBs)\==CBs then do; say; say center(' board' boards" ", 79, '▒'); end
@.=.; !.=@. /*initialize the chessboard to be empty*/
do p=1 for random(2, 32) /*generate a random number of chessmen.*/
if p<3 then call piece 'k' /*a king of each color. */
else call piece substr('bnpqr', random(1, 5), 1)
end /*p*/ /* [↑] place a piece on the chessboard*/
call cb /*display the ChessBoard and its FEN.*/
end /*boards*/ /* [↑] CB ≡ ─ ─ */
exit /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ cb: fen=; do r=8 for 8 by -1; $= /*the board rank (so far).*/
do f=8 for 8 by -1; $= $ || @.r.f /*append the board file. */
end /*f*/
say $ /*display the board rank. */
do e=8 for 8 by -1; $= changestr( copies(., e), $, e) /* . ≡ filler.*/
end /*e*/
fen= fen || $ || left('/', r\==1) /*append / if not 1st rank.*/
end /*r*/ /* [↑] append $ str to FEN*/
say /*display a blank sep. line*/
say 'FEN='fen "w - - 0 1" /*Forsyth─Edwards Notation.*/
return /* [↑] display chessboard.*/
/*──────────────────────────────────────────────────────────────────────────────────────*/ piece: parse arg x; if p//2 then upper x; arg ux /*use white if odd P.*/
if CBs<0 & p>2 then if random(1) then upper x /*CBs>0? Use balanced.*/
/*[↓] # isn't changed.*/
do #=0 by 0; r= random(1, 8); f= random(1, 8) /*random rank and file.*/
if @.r.f\==. then iterate /*is position occupied?*/
if (x=='p' & r==1) | (x=="P" & r==8) then iterate /*any promoting pawn? */
/*[↑] skip these pawns*/
if ux=='K' then do rr=r-1 for 3 /*[↓] neighbor ≡ king?*/
do ff=f-1 for 3; if !.rr.ff=='K' then iterate # /*king?*/
end /*rr*/ /*[↑] neighbor ≡ king?*/
end /*ff*/ /*[↑] we're all done. */
@.r.f= x /*put random piece. */
!.r.f= ux; return /* " " " upper*/
end /*#*/ /*#: isn't incremented.*/</lang>
Some older REXXes don't have a changestr BIF, so one is included here: ───► CHANGESTR.REX.
output showing five chess positions (starting with a specific position by seeding the random BIF with 96),
specifying the arguments (for Regina REXX under Windows): 96 5
▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ board 1 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ........ ........ ....K... ........ ....k... ........ ........ ........ FEN=8/8/4K3/8/4k3/8/8/8 w - - 0 1 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ board 2 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ...Q..r. r.kbn... ...pqn.p ..N.N.qQ p....N.n ..N..... ...NB... .R.Q.KBP FEN=3Q2r1/r1kbn3/3pqn1p/2N1N1qQ/p4N1n/2N5/3NB3/1R1Q1KBP w - - 0 1 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ board 3 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ .....B.n N...p.p. .q..n... .K..R... .BP...P. q....k.. ........ R.N..n.. FEN=5B1n/N3p1p1/1q2n3/1K2R3/1BP3P1/q4k2/8/R1N2n2 w - - 0 1 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ board 4 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ ......K. pN..q... ...qN... ....n... .....Q.. ........ ....k... P.r....B FEN=6K1/pN2q3/3qN3/4n3/5Q2/8/4k3/P1r4B w - - 0 1 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ board 5 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ qnqN...N ...B...N n....P.Q PP..b.Rn KqB..... pB.knp.. q.n.qB.. .......N FEN=qnqN3N/3B3N/n4P1Q/PP2b1Rn/KqB5/pB1knp2/q1n1qB2/7N w - - 0 1
Ruby
<lang ruby> def hasNK( board, a, b )
for g in -1 .. 1
for f in -1 .. 1
aa = a + f; bb = b + g
if aa.between?( 0, 7 ) && bb.between?( 0, 7 )
p = board[aa + 8 * bb]
if p == "K" || p == "k"; return true; end
end
end
end
return false
end def generateBoard( board, pieces )
while( pieces.length > 1 )
p = pieces[pieces.length - 1]
pieces = pieces[0...-1]
while( true )
a = rand( 8 ); b = rand( 8 )
if ( ( b == 0 || b == 7 ) && ( p == "P" || p == "p" ) ) ||
( ( p == "k" || p == "K" ) && hasNK( board, a, b ) ); next; end
if board[a + b * 8] == nil; break;end
end
board[a + b * 8] = p
end
end pieces = "ppppppppkqrrbbnnPPPPPPPPKQRRBBNN" for i in 0 .. 10
e = pieces.length - 1
while e > 0
p = rand( e ); t = pieces[e];
pieces[e] = pieces[p]; pieces[p] = t; e -= 1
end
end board = Array.new( 64 ); generateBoard( board, pieces ) puts e = 0 for j in 0 .. 7
for i in 0 .. 7
if board[i + 8 * j] == nil; e += 1
else
if e > 0; print( e ); e = 0; end
print( board[i + 8 * j] )
end
end
if e > 0; print( e ); e = 0; end
if j < 7; print( "/" ); end
end print( " w - - 0 1\n" ) for j in 0 .. 7
for i in 0 .. 7
if board[i + j * 8] == nil; print( "." )
else print( board[i + j * 8] ); end
end
puts
end </lang>
- Output:
1bN1RK2/1Pp1pQbP/p2PpP2/8/1pkNP3/P1r1Pp1p/Bn1RPp1r/3qB3 w - - 0 1 .bN.RK.. .Pp.pQbP p..PpP.. ........ .pkNP... P.r.Pp.p Bn.RPp.r ...qB...
Rust
<lang Rust>use std::fmt::Write;
use rand::{Rng, distributions::{Distribution, Standard}};
const EMPTY: u8 = b'.';
- [derive(Clone, Debug)]
struct Board {
grid: [[u8; 8]; 8],
}
impl Distribution<Board> for Standard {
fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> Board {
let mut board = Board::empty();
board.place_kings(rng);
board.place_pieces(rng, b"PPPPPPPP", true);
board.place_pieces(rng, b"pppppppp", true);
board.place_pieces(rng, b"RNBQBNR", false);
board.place_pieces(rng, b"rnbqbnr", false);
board
}
}
impl Board {
fn empty() -> Self {
Board { grid: [[EMPTY; 8]; 8] }
}
fn fen(&self) -> String {
let mut fen = String::new();
let mut count_empty = 0;
for row in &self.grid {
for &ch in row {
print!("{} ", ch as char);
if ch == EMPTY {
count_empty += 1;
} else {
if count_empty > 0 {
write!(fen, "{}", count_empty).unwrap();
count_empty = 0;
}
fen.push(ch as char);
}
}
if count_empty > 0 {
write!(fen, "{}", count_empty).unwrap();
count_empty = 0;
}
fen.push('/');
println!();
}
fen.push_str(" w - - 0 1");
fen
}
fn place_kings<R: Rng + ?Sized>(&mut self, rng: &mut R) {
loop {
let r1: i8 = rng.gen_range(0, 8);
let c1: i8 = rng.gen_range(0, 8);
let r2: i8 = rng.gen_range(0, 8);
let c2: i8 = rng.gen_range(0, 8);
if r1 != r2 && (r1 - r2).abs() > 1 && (c1 - c2).abs() > 1 {
self.grid[r1 as usize][c1 as usize] = b'K';
self.grid[r2 as usize][c2 as usize] = b'k';
return;
}
}
}
fn place_pieces<R: Rng + ?Sized>(&mut self, rng: &mut R, pieces: &[u8], is_pawn: bool) {
let num_to_place = rng.gen_range(0, pieces.len());
for &piece in pieces.iter().take(num_to_place) {
let mut r = rng.gen_range(0, 8);
let mut c = rng.gen_range(0, 8);
while self.grid[r][c] != EMPTY || (is_pawn && (r == 7 || r == 0)) {
r = rng.gen_range(0, 8);
c = rng.gen_range(0, 8);
}
self.grid[r][c] = piece;
}
}
}
fn main() {
let b: Board = rand::random();
println!("{}", b.fen());
}</lang>
- Output:
b . . . . . . . . R P . . . . . n . . P . . . k p . . . P r . . P p . b . . . n . . P . . . . . K . . . . . . . . . . q . . . . b7/1RP5/n2P3k/p3Pr2/Pp1b3n/2P5/K7/3q4/ w - - 0 1
Scala
- Output:
Best seen running in your browser Scastie (remote JVM).
<lang Scala>import scala.math.abs import scala.util.Random
object RandomFen extends App {
val rand = new Random
private def createFen = {
val grid = Array.ofDim[Char](8, 8)
def placeKings(grid: Array[Array[Char]]): Unit = {
var r1, c1, r2, c2 = 0
do {
r1 = rand.nextInt(8)
c1 = rand.nextInt(8)
r2 = rand.nextInt(8)
c2 = rand.nextInt(8)
} while (r1 == r2 || abs(r1 - r2) <= 1 || abs(c1 - c2) <= 1)
grid(r1)(c1) = 'K'
grid(r2)(c2) = 'k'
}
def placePieces(grid: Array[Array[Char]],
pieces: String,
isPawn: Boolean): Unit = {
val numToPlace = rand.nextInt(pieces.length)
for (n <- 0 until numToPlace) {
var r, c = 0
do {
r = rand.nextInt(8)
c = rand.nextInt(8)
} while (grid(r)(c) != 0 || (isPawn && (r == 7 || r == 0)))
grid(r)(c) = pieces(n)
}
}
def toFen(grid: Array[Array[Char]]) = {
val fen = new StringBuilder
var countEmpty = 0
for (r <- grid.indices) {
for (c <- grid.indices) {
val ch = grid(r)(c)
print(f"${if (ch == 0) '.' else ch}%2c ")
if (ch == 0) countEmpty += 1
else {
if (countEmpty > 0) {
fen.append(countEmpty)
countEmpty = 0
}
fen.append(ch)
}
}
if (countEmpty > 0) {
fen.append(countEmpty)
countEmpty = 0
}
fen.append("/")
println()
}
fen.append(" w - - 0 1").toString
}
placeKings(grid) placePieces(grid, "PPPPPPPP", isPawn = true) placePieces(grid, "pppppppp", isPawn = true) placePieces(grid, "RNBQBNR", isPawn = false) placePieces(grid, "rnbqbnr", isPawn = false) toFen(grid) }
println(createFen)
}</lang>
Typescript
<lang typescript> class Fen {
public createFen() {
let grid: string[][];
grid = [];
for (let r = 0; r < 8; r++) {
grid[r] = [];
for (let c = 0; c < 8; c++) {
grid[r][c] = "0";
}
}
this.placeKings(grid);
this.placePieces(grid, "PPPPPPPP", true);
this.placePieces(grid, "pppppppp", true);
this.placePieces(grid, "RNBQBNR", false);
this.placePieces(grid, "rnbqbnr", false);
return this.toFen(grid);
}
private placeKings(grid: string[][]): void {
let r1, c1, r2, c2: number;
while (true) {
r1 = Math.floor(Math.random() * 8);
c1 = Math.floor(Math.random() * 8);
r2 = Math.floor(Math.random() * 8);
c2 = Math.floor(Math.random() * 8);
if (r1 != r2 && Math.abs(r1 - r2) > 1 && Math.abs(c1 - c2) > 1) {
break;
}
}
grid[r1][c1] = "K";
grid[r2][c2] = "k";
}
private placePieces(grid: string[][], pieces: string, isPawn: boolean): void {
let numToPlace: number = Math.floor(Math.random() * pieces.length);
for (let n = 0; n < numToPlace; n++) {
let r, c: number;
do {
r = Math.floor(Math.random() * 8);
c = Math.floor(Math.random() * 8);
} while (grid[r][c] != "0" || (isPawn && (r == 7 || r == 0)));
grid[r][c] = pieces.charAt(n);
}
}
private toFen(grid: string[][]): string {
let result: string = "";
let countEmpty: number = 0;
for (let r = 0; r < 8; r++) {
for (let c = 0; c < 8; c++) {
let char: string = grid[r][c];
if (char == "0") {
countEmpty++;
} else {
if (countEmpty > 0) {
result += countEmpty;
countEmpty = 0;
}
result += char;
}
}
if (countEmpty > 0) {
result += countEmpty;
countEmpty = 0;
}
result += "/";
}
return result += " w - - 0 1";
}
}
let fen: Fen = new Fen(); console.log(fen.createFen()); </lang>
- Output:
5B2/2KbN3/pr6/pp6/5P2/5k2/1Rp5/1nQ5/ w - - 0 1
Wren
<lang ecmascript>import "random" for Random import "/fmt" for Fmt
var rand = Random.new()
var grid = List.filled(8, null) for (i in 0..7) grid[i] = List.filled(9, ".")
var placeKings = Fn.new {
while (true) {
var r1 = rand.int(8)
var c1 = rand.int(8)
var r2 = rand.int(8)
var c2 = rand.int(8)
if (r1 != r2 && (r1 - r2).abs > 1 && (c1 - c2).abs > 1) {
grid[r1][c1] = "K"
grid[r2][c2] = "k"
return
}
}
}
var placePieces = Fn.new { |pieces, isPawn|
var numToPlace = rand.int(pieces.count)
for (n in 0...numToPlace) {
var r
var c
while (true) {
r = rand.int(8)
c = rand.int(8)
if (grid[r][c] == "." && !(isPawn && (r == 7 || r == 0))) break
}
grid[r][c] = pieces[n]
}
}
var toFen = Fn.new {
var fen = ""
var countEmpty = 0
for (r in 0..7) {
for (c in 0..7) {
var ch = grid[r][c]
Fmt.write("$2s ", ch)
if (ch == ".") {
countEmpty = countEmpty + 1
} else {
if (countEmpty > 0) {
fen = fen + countEmpty.toString
countEmpty = 0
}
fen = fen + ch
}
}
if (countEmpty > 0) {
fen = fen + countEmpty.toString
countEmpty = 0
}
fen = fen + "/"
System.print()
}
return fen + " w - - 0 1"
}
var createFen = Fn.new {
placeKings.call()
placePieces.call("PPPPPPPP", true)
placePieces.call("pppppppp", true)
placePieces.call("RNBQBNR", false)
placePieces.call("rnbqbnr", false)
return toFen.call()
}
System.print(createFen.call())</lang>
- Output:
Sample position:
. . . N . Q R . . . . . . r p . K . . . p . P . . . . . . . . . . . p . . . k . p . . . . . . . . . p . . . P B . . . . . . . . 3N1QR1/5rp1/K3p1P1/8/2p3k1/p7/2p3PB/8/ w - - 0 1
Yabasic
<lang Yabasic>dim grid(8, 8)
sub placeKings()
local r1, r2, c1, c2
do
r1 = int(ran(8))
c1 = int(ran(8))
r2 = int(ran(8))
c2 = int(ran(8))
if (r1 <> r2 and abs(r1 - r2) > 1 and abs(c1 - c2) > 1) then
grid(r1, c1) = asc("K")
grid(r2, c2) = asc("k")
return
end if
loop
end sub
sub placePieces(pieces$, isPawn)
local n, r, c, numToPlace
numToPlace = int(ran(len(pieces$)))
for n = 0 to numToPlace-1
repeat
r = int(ran(8))
c = int(ran(8))
until(not(grid(r, c) or (isPawn and (r = 7 or r = 0))))
grid(r, c) = asc(mid$(pieces$, n, 1))
next
end sub
sub toFen()
local fen$, ch, r, c, countEmpty
for r = 0 to 8-1
for c = 0 to 8-1
ch = grid(r, c)
if ch then print chr$(ch); else print "."; end if
if not ch then
countEmpty = countEmpty + 1
else
if countEmpty then
fen$ = fen$ + chr$(countEmpty + 48)
countEmpty = 0
end if
fen$ = fen$ + chr$(ch)
end if
next
if countEmpty then
fen$ = fen$ + chr$(countEmpty + 48)
countEmpty = 0
end if
fen$ = fen$ + "/"
print
next
fen$ = fen$ + " w - - 0 1"
print fen$
end sub
sub createFen()
placeKings()
placePieces("PPPPPPPP", TRUE)
placePieces("pppppppp", TRUE)
placePieces("RNBQBNR", FALSE)
placePieces("rnbqbnr", FALSE)
toFen()
end sub
createFen() </lang>
zkl
<lang zkl>fcn pickFEN{
# First we chose how many pieces to place: 2 to 32
n := (0).random(2,33);
# Then we pick $n squares: first n of shuffle (0,1,2,3...63)
n = [0..63].walk().shuffle()[0,n];
# We try to find suitable king positions on non-adjacent squares.
# If we could not find any, we return recursively
kings := Walker.cproduct(n,n).filter1(fcn([(a,b)]){ // Cartesian product
a!=b and (a/8 - b/8).abs() or (a%8 - b%8).abs()>1
}); # (a,b) on success, False on fail
if(not kings) return(pickFEN()); // tail recursion
# We make a list of pieces we can pick (apart from the kings)
pieces,pnp,pnP := "p P n N b B r R q Q".split(" "), pieces-"p", pieces-"P";
# We make a list of two king symbols to pick randomly a black or white king
k := "K k".split(" ").shuffle();
[0..63].apply('wrap(sq){ # look at each square
if(kings.holds(sq)) k.pop();
else if(n.holds(sq)){
row,n,n2 := 7 - sq/8, (0).random(pieces.len()), (0).random(pnp.len());
if( row == 7) pnP[n2] // no white pawn in the promotion square else if(row == 0) pnp[n2] // no black pawn in the promotion square else pieces[n] // otherwise, any ole random piece
}
else "#" // empty square
})
.pump(List,T(Void.Read,7),"".append,subst) // chunkize into groups of 8 chars (1 row)
.concat("/") + " w - - 0 1"
} fcn subst(str){ // replace "#" with count of #s
re :=RegExp("#+");
while(re.search(str,1)){ n,m:=re.matched[0]; str=String(str[0,n],m,str[n+m,*]) }
str
}</lang> <lang zkl>do(5){ pickFEN().println() }</lang>
- Output:
b3rQBr/n2b1Q1q/1R6/1BQRQ2n/RnB2r2/q3b1nQ/1BqB1bBQ/2q1Q3 w - - 0 1 b7/5qqB/qb3B2/8/3b4/Q1n3r1/3B2Q1/n6r w - - 0 1 r2R3N/Q1n5/1N6/1N1R1RBB/8/Rn1b1r2/3QbNN1/2n3rQ w - - 0 1 5b2/1R6/r4b1q/3Q4/8/8/8/5b2 w - - 0 1 8/1BQ5/8/1q6/1q6/3B1Rq1/5b2/3N3R w - - 0 1