Last list item

Last list item is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Task

List = [6, 81, 243, 14, 25, 49, 123, 69, 11]
Find the two smallest items, remove them from the list, find their sum, and add the sum to the end of list.
Repeat until the list contains one element.
Show the steps and last item on this page.
Show the unsorted list in output in case "Without sort"

11l

Translation of: Python

<lang 11l>F add_least_reduce(&lis)

  L lis.len > 1
     V el1 = lis.pop(lis.index(min(lis)))
     V el2 = lis.pop(lis.index(min(lis)))
     lis.append(el1 + el2)
     print(‘Interim list: ’lis)
  R lis

V LIST = [6, 81, 243, 14, 25, 49, 123, 69, 11]

print(LIST‘ ==> ’add_least_reduce(&copy(LIST)))</lang>

Output:

Interim list: [81, 243, 14, 25, 49, 123, 69, 17]
Interim list: [81, 243, 25, 49, 123, 69, 31]
Interim list: [81, 243, 49, 123, 69, 56]
Interim list: [81, 243, 123, 69, 105]
Interim list: [243, 123, 105, 150]
Interim list: [243, 150, 228]
Interim list: [243, 378]
Interim list: [621]
[6, 81, 243, 14, 25, 49, 123, 69, 11]  ==>  [621]

ALGOL 68

With sorting

Translation of: Wren

Library: ALGOL 68-rows

<lang algol68>BEGIN # find the last element after repeatedely adding the sum #

     # of the two smallest elements and removing them #
   PR read "rows.incl.a68" PR # row related utilities #

   [ 1 : 9 ]INT a := ( 6, 81, 243, 14, 25, 49, 123, 69, 11 );
   INT a count := UPB a;
   WHILE a count > 1 DO
       QUICKSORT a FROMELEMENT LWB a TOELEMENT a count;
       print( ( "Sorted list:" ) );FOR i TO a count DO print( ( " ", whole( a[ i ], 0 ) ) ) OD;
       INT sum = a[ 1 ] + a[ 2 ];
       print( ( "; two smallest: " , whole( a[ 1 ], 0 )
              , " + ", whole( a[ 2 ], 0 )
              , " = ", whole( sum, 0 )
              , newline
              )
            );
       a[ 1 : a count - 2 ] := a[ 3 : a count ];
       a count     -:= 1  ;
       a[ a count ] := sum
   OD;
   print( ( "Last item is ", whole( a[ 1 ], 0 ), ".", newline ) )

END</lang>

Output:

Sorted list: 6 11 14 25 49 69 81 123 243; two smallest: 6 + 11 = 17
Sorted list: 14 17 25 49 69 81 123 243; two smallest: 14 + 17 = 31
Sorted list: 25 31 49 69 81 123 243; two smallest: 25 + 31 = 56
Sorted list: 49 56 69 81 123 243; two smallest: 49 + 56 = 105
Sorted list: 69 81 105 123 243; two smallest: 69 + 81 = 150
Sorted list: 105 123 150 243; two smallest: 105 + 123 = 228
Sorted list: 150 228 243; two smallest: 150 + 228 = 378
Sorted list: 243 378; two smallest: 243 + 378 = 621
Last item is 621.

Without sorting

Translation of the sorted Wren version with the sorting removed. <lang algol68>BEGIN # find the last element after repeatedly adding the sum #

     # of the two smallest elements and removing them #
   [ 1 : 9 ]INT a := ( 6, 81, 243, 14, 25, 49, 123, 69, 11 );
   INT a count := UPB a;
   WHILE a count > 1 DO
       print( ( "List:" ) );FOR i TO a count DO print( ( " ", whole( a[ i ], 0 ) ) ) OD;
       INT s1pos, s2pos;
       IF a[ 1 ] < a[ 2 ]
       THEN s1pos := 1; s2pos := 2
       ELSE s1pos := 2; s2pos := 1
       FI;
       FOR i FROM 3 TO a count DO
           IF   a[ i ] < a[ s1pos ] THEN s2pos := s1pos; s1pos := i
           ELIF a[ i ] < a[ s2pos ] THEN s2pos := i
           FI
       OD;
       INT sum = a[ s1pos ] + a[ s2pos ];
       print( ( "; two smallest: " , whole( a[ s1pos ], 0 ), " @ ", whole( s1pos, 0 )
              , " and ",             whole( a[ s2pos ], 0 ), " @ ", whole( s2pos, 0 )
              , "; sum = ", whole( sum, 0 )
              , newline
              )
            );
       INT m pos := 0;
       FOR i TO a count DO
           IF i /= s1pos AND i /= s2pos THEN a[ m pos +:= 1 ] := a[ i ] FI
       OD;
       a[ m pos + 1 ] := sum;
       a count -:= 1  
   OD;
   print( ( "Last item is ", whole( a[ 1 ], 0 ), ".", newline ) )

END</lang>

Output:

List: 6 81 243 14 25 49 123 69 11; two smallest: 6 @ 1 and 11 @ 9; sum = 17
List: 81 243 14 25 49 123 69 17; two smallest: 14 @ 3 and 17 @ 8; sum = 31
List: 81 243 25 49 123 69 31; two smallest: 25 @ 3 and 31 @ 7; sum = 56
List: 81 243 49 123 69 56; two smallest: 49 @ 3 and 56 @ 6; sum = 105
List: 81 243 123 69 105; two smallest: 69 @ 4 and 81 @ 1; sum = 150
List: 243 123 105 150; two smallest: 105 @ 3 and 123 @ 2; sum = 228
List: 243 150 228; two smallest: 150 @ 2 and 228 @ 3; sum = 378
List: 243 378; two smallest: 243 @ 1 and 378 @ 2; sum = 621
Last item is 621.

AutoHotkey

<lang AutoHotkey>List := [6, 81, 243, 14, 25, 49, 123, 69, 11] steps := "Initial List `t`t`t" List2str(List) "`n" while List.Count() > 1 {

   sum := 0, str := ""
   loop 2
   {
       num := min(List*)
       sum += num 
       removeFromList(List, num)
       str .= (!str ? "2 smallest numbers: " : " + ") num 
   }
   List.Push(sum)
   steps .= str " = " sum "`t" List2str(List) "`n"

} MsgBox % result := steps return

removeFromList(ByRef List, num){

   for i, v in List
       if (v = num)
       {
           List.RemoveAt(i)
           break
       }

} List2str(List){

   for i, v in List
       unsorted_List .= v ", "
   return "[" Trim(unsorted_List, ", ") "]"

}</lang>

Output:

Initial List 				[6, 81, 243, 14, 25, 49, 123, 69, 11]
2 smallest numbers: 6 + 11 = 17		[81, 243, 14, 25, 49, 123, 69, 17]
2 smallest numbers: 14 + 17 = 31	[81, 243, 25, 49, 123, 69, 31]
2 smallest numbers: 25 + 31 = 56	[81, 243, 49, 123, 69, 56]
2 smallest numbers: 49 + 56 = 105	[81, 243, 123, 69, 105]
2 smallest numbers: 69 + 81 = 150	[243, 123, 105, 150]
2 smallest numbers: 105 + 123 = 228	[243, 150, 228]
2 smallest numbers: 150 + 228 = 378	[243, 378]
2 smallest numbers: 243 + 378 = 621	[621]

AWK

<lang AWK>

1. syntax: GAWK -f LAST_LIST_ITEM.AWK

BEGIN {

   split("6,81,243,14,25,49,123,69,11",arr1,",")
   PROCINFO["sorted_in"] = "@val_num_asc"
   while (length(arr1) > 1) {
     for (i in arr1) { printf("%s ",arr1[i]) } # show sorted list
     j = 0
     delete arr2
     for (i in arr1) { arr2[++j] = arr1[i] } # copy arr1 into arr2
     sum = arr2[1] + arr2[2]
     printf(": %s+%s=%s\n",arr2[1],arr2[2],sum)
     delete arr2[2]
     arr2[1] = sum
     delete arr1
     for (i in arr2) { arr1[i] = arr2[i] } # copy arr2 into arr1
   }
   printf("sum=%d\n",sum)
   exit(0)

} </lang>

Output:

6 11 14 25 49 69 81 123 243 : 6+11=17
14 17 25 49 69 81 123 243 : 14+17=31
25 31 49 69 81 123 243 : 25+31=56
49 56 69 81 123 243 : 49+56=105
69 81 105 123 243 : 69+81=150
105 123 150 243 : 105+123=228
150 228 243 : 150+228=378
243 378 : 243+378=621
sum=621

BQN

With and without sorting

<lang bqn>list ← ⟨6, 81, 243, 14, 25, 49, 123, 69, 11⟩

W_sort ← {{i←2↑∧𝕩, (𝕩/˜¬𝕩∊i)∾+´i}⍟(↕≠𝕩)𝕩}

WO_sort ← {{m←⌊´𝕩, n←⌊´𝕩/˜¬m=𝕩, (𝕩/˜¬𝕩∊m‿n)∾m+n}⍟(↕≠𝕩)𝕩}

•Show¨W_sort list •Show¨WO_sort list</lang> <lang>⟨ 6 81 243 14 25 49 123 69 11 ⟩ ⟨ 81 243 14 25 49 123 69 17 ⟩ ⟨ 81 243 25 49 123 69 31 ⟩ ⟨ 81 243 49 123 69 56 ⟩ ⟨ 81 243 123 69 105 ⟩ ⟨ 243 123 105 150 ⟩ ⟨ 243 150 228 ⟩ ⟨ 243 378 ⟩ ⟨ 621 ⟩ ⟨ 6 81 243 14 25 49 123 69 11 ⟩ ⟨ 81 243 14 25 49 123 69 17 ⟩ ⟨ 81 243 25 49 123 69 31 ⟩ ⟨ 81 243 49 123 69 56 ⟩ ⟨ 81 243 123 69 105 ⟩ ⟨ 243 123 105 150 ⟩ ⟨ 243 150 228 ⟩ ⟨ 243 378 ⟩ ⟨ 621 ⟩</lang>

C

With sorting

Translation of: Wren

<lang c>#include <stdio.h>

1. include <stdlib.h>

int compare(const void *a, const void *b) {

   int aa = *(const int *)a;
   int bb = *(const int *)b;
   if (aa < bb) return -1;
   if (aa > bb) return 1;
   return 0;

}

int main() {

   int a[] = {6, 81, 243, 14, 25, 49, 123, 69, 11};
   int isize = sizeof(int);
   int asize = sizeof(a) / isize;
   int i, sum;
   while (asize > 1) {
       qsort(a, asize, isize, compare);
       printf("Sorted list: ");
       for (i = 0; i < asize; ++i) printf("%d ", a[i]);
       printf("\n");
       sum = a[0] + a[1];
       printf("Two smallest: %d + %d = %d\n", a[0], a[1], sum);
       for (i = 2; i < asize; ++i) a[i-2] = a[i];
       a[asize - 2] = sum;
       asize--;
   }
   printf("Last item is %d.\n", a[0]);
   return 0;

}</lang>

Output:

Sorted list: 6 11 14 25 49 69 81 123 243 
Two smallest: 6 + 11 = 17
Sorted list: 14 17 25 49 69 81 123 243 
Two smallest: 14 + 17 = 31
Sorted list: 25 31 49 69 81 123 243 
Two smallest: 25 + 31 = 56
Sorted list: 49 56 69 81 123 243 
Two smallest: 49 + 56 = 105
Sorted list: 69 81 105 123 243 
Two smallest: 69 + 81 = 150
Sorted list: 105 123 150 243 
Two smallest: 105 + 123 = 228
Sorted list: 150 228 243 
Two smallest: 150 + 228 = 378
Sorted list: 243 378 
Two smallest: 243 + 378 = 621
Last item is 621.

Without sorting

<lang c>#include <stdio.h>

int findMin(int a[], int asize, int *pmin) {

   int i, ix = 0;
   *pmin = a[0];
   for (i = 0; i < asize; ++i) {
       if (a[i] < *pmin) {
           ix = i;
           *pmin = a[i];
       }
   }
   return ix;

}

int main() {

   int a[] = {6, 81, 243, 14, 25, 49, 123, 69, 11};
   int isize = sizeof(int);
   int asize = sizeof(a) / isize;
   int i, j, sum, ix, min = 0, s[2];
   while (asize > 1) {
       printf("List: ");
       for (i = 0; i < asize; ++i) printf("%d ", a[i]);
       printf("\n");
       for (i = 0; i < 2; ++i) {
           ix = findMin(a, asize, &min);
           s[i] = min;
           for (j = ix+1; j < asize; ++j) a[j-1] = a[j];
           asize--;
       }
       sum = s[0] + s[1];
       printf("Two smallest: %d + %d = %d\n", s[0], s[1], sum);
       a[asize] = sum;
       asize++;
   }
   printf("Last item is %d.\n", a[0]);
   return 0;

}</lang>

Output:

List: 6 81 243 14 25 49 123 69 11 
Two smallest: 6 + 11 = 17
List: 81 243 14 25 49 123 69 17 
Two smallest: 14 + 17 = 31
List: 81 243 25 49 123 69 31 
Two smallest: 25 + 31 = 56
List: 81 243 49 123 69 56 
Two smallest: 49 + 56 = 105
List: 81 243 123 69 105 
Two smallest: 69 + 81 = 150
List: 243 123 105 150 
Two smallest: 105 + 123 = 228
List: 243 150 228 
Two smallest: 150 + 228 = 378
List: 243 378 
Two smallest: 243 + 378 = 621
Last item is 621.

Factor

Works with: Factor version 0.99 2021-06-02

<lang factor>USING: formatting io kernel math math.statistics prettyprint sequences sequences.extras ;

list. ( seq -- )

   "List: " write [ bl ] [ pprint ] interleave nl ;

smallest. ( seq -- )

   first2 2dup + "Two smallest: %d + %d = %d\n" printf ;

remove-all-first! ( seq elts -- seq' )

   [ swap remove-first! ] each ;

step ( seq -- seq' )

   dup { 0 1 } kth-smallests tuck remove-all-first! over
   smallest. swap sum suffix! ;
   

V{ 6 81 243 14 25 49 123 69 11 } [ dup length 1 > ] [ dup list. step ] while last "Last item is %d.\n" printf</lang>

Output:

List: 6 81 243 14 25 49 123 69 11
Two smallest: 6 + 11 = 17
List: 81 243 14 25 49 123 69 17
Two smallest: 14 + 17 = 31
List: 81 243 25 49 123 69 31
Two smallest: 25 + 31 = 56
List: 81 243 49 123 69 56
Two smallest: 49 + 56 = 105
List: 81 243 123 69 105
Two smallest: 69 + 81 = 150
List: 243 123 105 150
Two smallest: 105 + 123 = 228
List: 243 150 228
Two smallest: 150 + 228 = 378
List: 243 378
Two smallest: 243 + 378 = 621
Last item is 621.

FreeBASIC

<lang freebasic>#define HUGE 99999999

redim as integer list(0 to 8) list(0) = 6 :list(1) = 81:list(2) = 243:list(3) = 14:list(4) = 25:list(5) = 49:list(6) = 123:list(7) = 69:list(8) = 11 dim as integer s, si, ss, ssi, i

for i = 0 to ubound(list)

   print list(i);" ";

next i print while ubound(list) > 0

   s = HUGE
   ss = HUGE
   for i = 0 to ubound(list)
       if list(i)<s then
           ss = s
           ssi = si
           s = list(i)
           si = i
       elseif list(i)<ss then
           ss = list(i)
           ssi = i
       end if
   next i
   if ss<s then swap s, ss
   for i = si to ubound(list)-1
       list(i) = list(i+1)
   next i
   for i = ssi to ubound(list)-2
       list(i) = list(i+1)
   next i
   list(ubound(list)-1) = s+ss
   redim preserve list(0 to ubound(list)-1)
   for i = 0 to ubound(list)
       print list(i);" ";
   next i
   print

wend</lang>

Output:

6  81  243  14  25  49  123  69  11 
81  243  14  25  49  123  69  17 
81  243  25  49  123  69  31 
81  243  49  123  69  56 
81  243  123  69  105 
243  123  105  150 
243  150  228 
243  378 
621

Go

Translation of: Wren

With sorting

<lang go>package main

import (

   "fmt"
   "sort"

)

func main() {

   a := []int{6, 81, 243, 14, 25, 49, 123, 69, 11}
   for len(a) > 1 {
       sort.Ints(a)
       fmt.Println("Sorted list:", a)
       sum := a[0] + a[1]
       fmt.Printf("Two smallest: %d + %d = %d\n", a[0], a[1], sum)
       a = append(a, sum)
       a = a[2:]
   }
   fmt.Println("Last item is", a[0], "\b.")

}</lang>

Output:

Sorted list: [6 11 14 25 49 69 81 123 243]
Two smallest: 6 + 11 = 17
Sorted list: [14 17 25 49 69 81 123 243]
Two smallest: 14 + 17 = 31
Sorted list: [25 31 49 69 81 123 243]
Two smallest: 25 + 31 = 56
Sorted list: [49 56 69 81 123 243]
Two smallest: 49 + 56 = 105
Sorted list: [69 81 105 123 243]
Two smallest: 69 + 81 = 150
Sorted list: [105 123 150 243]
Two smallest: 105 + 123 = 228
Sorted list: [150 228 243]
Two smallest: 150 + 228 = 378
Sorted list: [243 378]
Two smallest: 243 + 378 = 621
Last item is 621.

Without sorting

<lang go>package main

import "fmt"

func findMin(a []int) (int, int) {

   ix := 0
   min := a[0]
   for i := 1; i < len(a); i++ {
       if a[i] < min {
           ix = i
           min = a[i]
       }
   }
   return min, ix

}

func main() {

   a := []int{6, 81, 243, 14, 25, 49, 123, 69, 11}
   for len(a) > 1 {
       fmt.Println("List:", a)
       var s [2]int
       for i := 0; i < 2; i++ {
           min, ix := findMin(a)
           s[i] = min
           a = append(a[:ix], a[ix+1:]...)
       }
       sum := s[0] + s[1]
       fmt.Printf("Two smallest: %d + %d = %d\n", s[0], s[1], sum)
       a = append(a, sum)
   }
   fmt.Println("Last item is", a[0], "\b.")

}</lang>

Output:

List: [6 81 243 14 25 49 123 69 11]
Two smallest: 6 + 11 = 17
List: [81 243 14 25 49 123 69 17]
Two smallest: 14 + 17 = 31
List: [81 243 25 49 123 69 31]
Two smallest: 25 + 31 = 56
List: [81 243 49 123 69 56]
Two smallest: 49 + 56 = 105
List: [81 243 123 69 105]
Two smallest: 69 + 81 = 150
List: [243 123 105 150]
Two smallest: 105 + 123 = 228
List: [243 150 228]
Two smallest: 150 + 228 = 378
List: [243 378]
Two smallest: 243 + 378 = 621
Last item is 621.

jq

Adapted from Wren

Works with: jq

Works with gojq, the Go implementation of jq

With sorting

<lang jq>def task_with_sorting:

 foreach range(1; length) as $i ( {a: .};
     .a |= sort
     | .emit = "Sorted list: \(.a)\n"
     | (.a[0] + .a[1]) as $sum
     | .emit += "Two smallest: \(.a[0]) + \(.a[1]) = \($sum)"
     | .a += [$sum]
     | .a |= .[2:] ;
  .emit,
  (select(.a|length==1) | "Last item is \(.a[0]).") );

[6, 81, 243, 14, 25, 49, 123, 69, 11] | task_with_sorting</lang>

Output:

Sorted list: [6,11,14,25,49,69,81,123,243]
Two smallest: 6 + 11 = 17
Sorted list: [14,17,25,49,69,81,123,243]
Two smallest: 14 + 17 = 31
Sorted list: [25,31,49,69,81,123,243]
Two smallest: 25 + 31 = 56
Sorted list: [49,56,69,81,123,243]
Two smallest: 49 + 56 = 105
Sorted list: [69,81,105,123,243]
Two smallest: 69 + 81 = 150
Sorted list: [105,123,150,243]
Two smallest: 105 + 123 = 228
Sorted list: [150,228,243]
Two smallest: 150 + 228 = 378
Sorted list: [243,378]
Two smallest: 243 + 378 = 621
Last item is 621.

Without sorting

<lang jq>def min_index:

 . as $in
 | reduce range(0; length) as $i ( null;
    $in[$i] as $x 
    | if . == null then {ix: 0, min: $x}
      elif $x < .min then {ix: $i, min: $x}
      else . end)
 | .ix;
  

def task_without_sorting:

 # Output: [min, remainder]
 def remove_min:
    min_index as $ix
    | [.[$ix], (.[:$ix] + .[$ix + 1:])];

 foreach range(1; length) as $i ( {a: .};
      .emit = "Unsorted list: \(.a)\n"
    | (.a | remove_min) as [$m1, $x]
    | ($x | remove_min) as [$m2, $y]
    | ($m1 + $m2) as $sum
    | .emit += "Two smallest: \($m1) + \($m2) = \($sum)"
    | .a = $y + [$sum] ;
    .emit,
  (select(.a|length==1) | "Last item is \(.a[0]).") );

[6, 81, 243, 14, 25, 49, 123, 69, 11] | task_without_sorting </lang>

Output:

Unsorted list: [6,81,243,14,25,49,123,69,11]
Two smallest: 6 + 11 = 17
Unsorted list: [81,243,14,25,49,123,69,17]
Two smallest: 14 + 17 = 31
Unsorted list: [81,243,25,49,123,69,31]
Two smallest: 25 + 31 = 56
Unsorted list: [81,243,49,123,69,56]
Two smallest: 49 + 56 = 105
Unsorted list: [81,243,123,69,105]
Two smallest: 69 + 81 = 150
Unsorted list: [243,123,105,150]
Two smallest: 105 + 123 = 228
Unsorted list: [243,150,228]
Two smallest: 150 + 228 = 378
Unsorted list: [243,378]
Two smallest: 243 + 378 = 621
Last item is 621.

Julia

<lang julia>list = [6, 81, 243, 14, 25, 49, 123, 69, 11]

function addleastreduce!(lis)

   while length(lis) > 1
        push!(lis, popat!(lis, last(findmin(lis))) + popat!(lis, last(findmin(lis))))
        println("Interim list: $lis")
   end
   return lis

end

@show list, addleastreduce!(copy(list))

</lang>

Output:

Interim list: [81, 243, 14, 25, 49, 123, 69, 17]
Interim list: [81, 243, 25, 49, 123, 69, 31]
Interim list: [81, 243, 49, 123, 69, 56]
Interim list: [81, 243, 123, 69, 105]
Interim list: [243, 123, 105, 150]
Interim list: [243, 150, 228]
Interim list: [243, 378]
Interim list: [621]
(list, addleastreduce!(copy(list))) = ([6, 81, 243, 14, 25, 49, 123, 69, 11], [621])

Nim

With sorting

We sort in descending order as it is more efficient. <lang Nim># With sorting. import algorithm, strformat

proc extractAndAddTwoSmallest(list: var seq[int]) =

 list.sort(Descending)
 stdout.write &"Descending sorted list: {list}"
 let min1 = list.pop()
 let min2 = list.pop()
 echo &"; two smallest: {min1} and {min2}; sum = {min1 + min2}"
 list.add min1 + min2

var list = @[6, 81, 243, 14, 25, 49, 123, 69, 11]

while list.len >= 2:

 list.extractAndAddTwoSmallest()

echo &"Last item is {list[0]}."</lang>

Output:

Descending sorted list: @[243, 123, 81, 69, 49, 25, 14, 11, 6]; two smallest: 6 and 11; sum = 17
Descending sorted list: @[243, 123, 81, 69, 49, 25, 17, 14]; two smallest: 14 and 17; sum = 31
Descending sorted list: @[243, 123, 81, 69, 49, 31, 25]; two smallest: 25 and 31; sum = 56
Descending sorted list: @[243, 123, 81, 69, 56, 49]; two smallest: 49 and 56; sum = 105
Descending sorted list: @[243, 123, 105, 81, 69]; two smallest: 69 and 81; sum = 150
Descending sorted list: @[243, 150, 123, 105]; two smallest: 105 and 123; sum = 228
Descending sorted list: @[243, 228, 150]; two smallest: 150 and 228; sum = 378
Descending sorted list: @[378, 243]; two smallest: 243 and 378; sum = 621
Last item is 621.

Without sorting

We could use the function minIndex from module sequtils but it would be less efficient. We used a single loop instead. Please note that we remove the elements using function del which is O(1) rather than function delete which is O(n).

<lang Nim># Without sorting. import strformat

proc extractAndAddTwoSmallest(list: var seq[int]) =

 var min1, min2 = int.high
 var imin1, imin2 = -1
 for i, val in list:
   if val < min1:
     min2 = min1
     min1 = val
     imin2 = imin1
     imin1 = i
   elif val < min2:
     min2 = val
     imin2 = i
 echo &"List: {list}; two smallest: {min1}@{imin1} and {min2}@{imin2}; sum = {min1 + min2}"
 if imin1 > imin2: swap imin1, imin2   # Make sure "imin2" is the greatest index.
 list.del imin2
 list.del imin1
 list.add min1 + min2

var list = @[6, 81, 243, 14, 25, 49, 123, 69, 11]

while list.len >= 2:

 list.extractAndAddTwoSmallest()

echo &"Last item is {list[0]}."</lang>

Output:

List: @[6, 81, 243, 14, 25, 49, 123, 69, 11]; two smallest: 6@0 and 11@8; sum = 17
List: @[69, 81, 243, 14, 25, 49, 123, 17]; two smallest: 14@3 and 17@7; sum = 31
List: @[69, 81, 243, 123, 25, 49, 31]; two smallest: 25@4 and 31@6; sum = 56
List: @[69, 81, 243, 123, 49, 56]; two smallest: 49@4 and 56@5; sum = 105
List: @[69, 81, 243, 123, 105]; two smallest: 69@0 and 81@1; sum = 150
List: @[123, 105, 243, 150]; two smallest: 105@1 and 123@0; sum = 228
List: @[243, 150, 228]; two smallest: 150@1 and 228@2; sum = 378
List: @[243, 378]; two smallest: 243@0 and 378@1; sum = 621
Last item is 621.

Perl

Translation of: Raku

<lang perl>use strict; use warnings; use feature 'say'; use List::AllUtils <min firstidx>;

my @list = <6 81 243 14 25 49 123 69 11>; say " Original @list"; push @list, get(min @list) + get(min @list) and say "@list" while @list > 1;

sub get {

   my($min) = @_;
   splice @list, (firstidx { $min == $_ } @list), 1;
   printf " %3d ", $min;
   $min;

}</lang>

Output:

 Original 6 81 243 14 25 49 123 69 11
   6   11 81 243 14 25 49 123 69 17
  14   17 81 243 25 49 123 69 31
  25   31 81 243 49 123 69 56
  49   56 81 243 123 69 105
  69   81 243 123 105 150
 105  123 243 150 228
 150  228 243 378
 243  378 621

Phix

With sorting

with javascript_semantics
sequence list = {6, 81, 243, 14, 25, 49, 123, 69, 11}
while length(list)>1 do
    list = sort(deep_copy(list))
    integer l1 = list[1], l2 = list[2], l12 = l1+l2
    printf(1,"Sorted list: %V, two smallest: %d + %d = %d\n",{list,l1,l2,l12})
    list[1..2] = {l12}
end while
printf(1,"Last item is %d\n",list)

Output:

Sorted list: {6,11,14,25,49,69,81,123,243}, two smallest: 6 + 11 = 17
Sorted list: {14,17,25,49,69,81,123,243}, two smallest: 14 + 17 = 31
Sorted list: {25,31,49,69,81,123,243}, two smallest: 25 + 31 = 56
Sorted list: {49,56,69,81,123,243}, two smallest: 49 + 56 = 105
Sorted list: {69,81,105,123,243}, two smallest: 69 + 81 = 150
Sorted list: {105,123,150,243}, two smallest: 105 + 123 = 228
Sorted list: {150,228,243}, two smallest: 150 + 228 = 378
Sorted list: {243,378}, two smallest: 243 + 378 = 621
Last item is 621

Without sorting

with javascript_semantics
sequence list = {6, 81, 243, 14, 25, 49, 123, 69, 11}
while length(list)>1 do
    printf(1,"List: %V, two smallest: ",{list})
    integer l1, l2 = 0
    for i=1 to 2 do
        l1 = l2
        integer ldx = smallest(list,true)
        l2 = list[ldx]
        list = list[1..ldx-1] & list[ldx+1..$]
    end for
    printf(1,"%d + %d = %d\n",{l1,l2,l1+l2})
    list &= l1+l2
end while
printf(1,"Last item is %d\n",list)

Output:

List: {6,81,243,14,25,49,123,69,11}, two smallest: 6 + 11 = 17
List: {81,243,14,25,49,123,69,17}, two smallest: 14 + 17 = 31
List: {81,243,25,49,123,69,31}, two smallest: 25 + 31 = 56
List: {81,243,49,123,69,56}, two smallest: 49 + 56 = 105
List: {81,243,123,69,105}, two smallest: 69 + 81 = 150
List: {243,123,105,150}, two smallest: 105 + 123 = 228
List: {243,150,228}, two smallest: 150 + 228 = 378
List: {243,378}, two smallest: 243 + 378 = 621
Last item is 621

Python

Translation of: Julia

<lang python>""" Rosetta code task: Last list item """

def add_least_reduce(lis):

   """ Reduce lis: sum least two elements adding sum to list. Will take len(list) - 1 steps """
   while len(lis) > 1:
       lis.append(lis.pop(lis.index(min(lis))) + lis.pop(lis.index(min(lis))))
       print('Interim list:', lis)
   return lis

LIST = [6, 81, 243, 14, 25, 49, 123, 69, 11]

print(LIST, ' ==> ', add_least_reduce(LIST.copy()))

</lang>

Output:

Interim list: [81, 243, 14, 25, 49, 123, 69, 17]
Interim list: [81, 243, 25, 49, 123, 69, 31]
Interim list: [81, 243, 49, 123, 69, 56]
Interim list: [81, 243, 123, 69, 105]
Interim list: [243, 123, 105, 150]
Interim list: [243, 150, 228]
Interim list: [243, 378]
Interim list: [621]
[6, 81, 243, 14, 25, 49, 123, 69, 11]  ==>  [621]

Raku

Uses no sorting; does not modify overall list order while processing. <lang perl6>say ' Original ', my @list = 6, 81, 243, 14, 25, 49, 123, 69, 11;

say push @list: get(min @list) + get(min @list) while @list > 1;

sub get ($min) {

   @list.splice: @list.first(* == $min, :k), 1;
   printf " %3d ", $min;
   $min;

}</lang>

Output:

 Original [6 81 243 14 25 49 123 69 11]
   6   11 [81 243 14 25 49 123 69 17]
  14   17 [81 243 25 49 123 69 31]
  25   31 [81 243 49 123 69 56]
  49   56 [81 243 123 69 105]
  69   81 [243 123 105 150]
 105  123 [243 150 228]
 150  228 [243 378]
 243  378 [621]

REXX

With sorting

<lang rexx>/* REXX */ List = '6 81 243 14 25 49 123 69 11' Do Until words(list)=1

 list=wordsort(list)
 Say 'Sorted list:' list
 Parse Var list a b c
 Say 'Two smallest:' a '+' b '=' (a+b)
 list=(a+b) c
 End

Say 'Last item:' list Exit wordsort: Procedure /**********************************************************************

• Sort the list of words supplied as argument. Return the sorted list
  • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • /

 Parse Arg wl
 wa.=
 wa.0=0
 Do While wl<>
   Parse Var wl w wl
   Do i=1 To wa.0
     If wa.i>w Then Leave
     End
   If i<=wa.0 Then Do
     Do j=wa.0 To i By -1
       ii=j+1
       wa.ii=wa.j
       End
     End
   wa.i=w
   wa.0=wa.0+1
   End
 swl=
 Do i=1 To wa.0
   swl=swl wa.i
   End
 Return strip(swl)</lang>

Output:

Sorted list: 6 11 14 25 49 69 81 123 243
Two smallest: 6 + 11 = 17
Sorted list: 14 17 25 49 69 81 123 243
Two smallest: 14 + 17 = 31
Sorted list: 25 31 49 69 81 123 243
Two smallest: 25 + 31 = 56
Sorted list: 49 56 69 81 123 243
Two smallest: 49 + 56 = 105
Sorted list: 69 81 105 123 243
Two smallest: 69 + 81 = 150
Sorted list: 105 123 150 243
Two smallest: 105 + 123 = 228
Sorted list: 150 228 243
Two smallest: 150 + 228 = 378
Sorted list: 243 378
Two smallest: 243 + 378 = 621
Last item: 621

Without sorting

<lang rexx>/* REXX */ List = '6 81 243 14 25 49 123 69 11' Do Until words(list)=1

 Say 'List:' list
 a=getmin()
 b=getmin()
 Say 'Two smallest:' a '+' b '=' (a+b)
 list=list (a+b)
 End

Say 'Last item:' list Exit

getmin: Procedure Expose list /* Return the smallest element of list and remove it from list */ min=1e9 Do i=1 To words(list)

 If word(list,i)<min Then Do
   m=word(list,i)
   min=m
   j=i
   End
 End

list=subword(list,1,j-1) subword(list,j+1) Return m</lang>

Output:

List: 6 81 243 14 25 49 123 69 11
Two smallest: 6 + 11 = 17
List: 81 243 14 25 49 123 69  17
Two smallest: 14 + 17 = 31
List: 81 243 25 49 123 69  31
Two smallest: 25 + 31 = 56
List: 81 243 49 123 69  56
Two smallest: 49 + 56 = 105
List: 81 243 123 69  105
Two smallest: 69 + 81 = 150
List:  243 123 105 150
Two smallest: 105 + 123 = 228
List: 243 150 228
Two smallest: 150 + 228 = 378
List: 243  378
Two smallest: 243 + 378 = 621
Last item:   621

Ring

With sorting

<lang ring> see "working..." + nl

List = [6,81,243,14,25,49,123,69,11] n = 0

while true

     n++
     List = sort(List)
     first = List[1]
     second = List[2]
     ind1 = find(List,first)
     ind2 = find(List,second)
     if ind1 < ind2
        del(List,ind2)
        del(List,ind1)
     else
        del(List,ind1)
        del(List,ind2)
     ok
     sum = first + second 
     add(List,sum)
     if len(List) = 1
        exit
     ok
     if n = 1
        see nl + "List = "
        showArray(List)
        see nl
     ok
     showList(first,second,sum,List)

end

see "Last item is: " +List[1] + nl see "done..." + nl

func showList(first,second,sum,List)

    see "two smallest is = " + first + " + " + second + " = " + sum + nl
    see "List = "
    showArray(List)     

func showArray(array)

    txt = ""
    see "["
    for n = 1 to len(array)
        txt = txt + array[n] + ","
    next
    txt = left(txt,len(txt)-1)
    txt = txt + "]"
    see txt + nl

</lang>

Output:

working...

List = [14,25,49,69,81,123,243,17]

two smallest is = 6 + 11 = 17
List = [14,25,49,69,81,123,243,17]
two smallest is = 14 + 17 = 31
List = [25,49,69,81,123,243,31]
two smallest is = 25 + 31 = 56
List = [49,69,81,123,243,56]
two smallest is = 49 + 56 = 105
List = [69,81,123,243,105]
two smallest is = 69 + 81 = 150
List = [105,123,243,150]
two smallest is = 105 + 123 = 228
List = [150,243,228]
two smallest is = 150 + 228 = 378
List = [243,378]
Last item is: 621
done...

Without sorting

<lang ring> see "working..." + nl

List = [6,81,243,14,25,49,123,69,11] n = 0

while true

     n++
     if n = 1
        see nl + "List = "
        showArray(List)
        see nl
     ok
     first = min(List)
     ind1 = find(List,first)
     del(List,ind1)
     second = min(List)
     ind2 = find(List,second)
     del(List,ind2)
     sum = first + second 
     add(List,sum)
     if len(List) = 1
        exit
     ok
     showList(first,second,sum,List)

end

see "Last item is: " +List[1] + nl see "done..." + nl

func showList(first,second,sum,List)

    see "two smallest is = " + first + " + " + second + " = " + sum + nl
    see "List = "
    showArray(List)     

func showArray(array)

    txt = ""
    see "["
    for n = 1 to len(array)
        txt = txt + array[n] + ","
    next
    txt = left(txt,len(txt)-1)
    txt = txt + "]"
    see txt + nl

</lang>

Output:

working...

List = [6,81,243,14,25,49,123,69,11]

two smallest is = 6 + 11 = 17
List = [81,243,14,25,49,123,69,17]
two smallest is = 14 + 17 = 31
List = [81,243,25,49,123,69,31]
two smallest is = 25 + 31 = 56
List = [81,243,49,123,69,56]
two smallest is = 49 + 56 = 105
List = [81,243,123,69,105]
two smallest is = 69 + 81 = 150
List = [243,123,105,150]
two smallest is = 105 + 123 = 228
List = [243,150,228]
two smallest is = 150 + 228 = 378
List = [243,378]
Last item is: 621
done...

=Sidef

With sorting

<lang ruby>var k = 2 var list = [6, 81, 243, 14, 25, 49, 123, 69, 11]

while (list.len >= k) {

   var a = list.sort!.shift(k)
   list << a.sum
   say "#{a.map{'%3s' % _}.join(' ')} : #{list}"

}</lang>

Output:

  6  11 : [14, 25, 49, 69, 81, 123, 243, 17]
 14  17 : [25, 49, 69, 81, 123, 243, 31]
 25  31 : [49, 69, 81, 123, 243, 56]
 49  56 : [69, 81, 123, 243, 105]
 69  81 : [105, 123, 243, 150]
105 123 : [150, 243, 228]
150 228 : [243, 378]
243 378 : [621]

Without sorting

<lang ruby>var k = 2 var list = [6, 81, 243, 14, 25, 49, 123, 69, 11]

while (list.len >= k) {

   var a = gather {
       k.times {
           take(var v = list.min)
           list.delete_first(v)
       }
   }

   list << a.sum
   say "#{a.map{'%3s' % _}.join(' ')} : #{list}"

}</lang>

Output:

  6  11 : [81, 243, 14, 25, 49, 123, 69, 17]
 14  17 : [81, 243, 25, 49, 123, 69, 31]
 25  31 : [81, 243, 49, 123, 69, 56]
 49  56 : [81, 243, 123, 69, 105]
 69  81 : [243, 123, 105, 150]
105 123 : [243, 150, 228]
150 228 : [243, 378]
243 378 : [621]

Wren

With sorting

<lang ecmascript>var a = [6, 81, 243, 14, 25, 49, 123, 69, 11]

while (a.count > 1) {

   a.sort()
   System.print("Sorted list: %(a)")
   var sum = a[0] + a[1]
   System.print("Two smallest: %(a[0]) + %(a[1]) = %(sum)")
   a.add(sum)
   a = a[2..-1]

}

System.print("Last item is %(a[0]).")</lang>

Output:

Sorted list: [6, 11, 14, 25, 49, 69, 81, 123, 243]
Two smallest: 6 + 11 = 17
Sorted list: [14, 17, 25, 49, 69, 81, 123, 243]
Two smallest: 14 + 17 = 31
Sorted list: [25, 31, 49, 69, 81, 123, 243]
Two smallest: 25 + 31 = 56
Sorted list: [49, 56, 69, 81, 123, 243]
Two smallest: 49 + 56 = 105
Sorted list: [69, 81, 105, 123, 243]
Two smallest: 69 + 81 = 150
Sorted list: [105, 123, 150, 243]
Two smallest: 105 + 123 = 228
Sorted list: [150, 228, 243]
Two smallest: 150 + 228 = 378
Sorted list: [243, 378]
Two smallest: 243 + 378 = 621
Last item is 621.

Without sorting

<lang ecmascript>var findMin = Fn.new { |a|

   var ix = 0
   var min = a[0]
   for (i in 1...a.count) {
       if (a[i] < min) {
           ix = i
           min = a[i]
       }
   }
   return [min, ix]

}

var a = [6, 81, 243, 14, 25, 49, 123, 69, 11]

while (a.count > 1) {

   System.print("List: %(a)")
   var s = List.filled(2, 0)
   for (i in 0..1) {
       var m = findMin.call(a)
       s[i] = m[0]
       a.removeAt(m[1])
   }
   var sum = s[0] + s[1]
   System.print("Two smallest: %(s[0]) + %(s[1]) = %(sum)")
   a.add(sum)

}

System.print("Last item is %(a[0]).")</lang>

Output:

List: [6, 81, 243, 14, 25, 49, 123, 69, 11]
Two smallest: 6 + 11 = 17
List: [81, 243, 14, 25, 49, 123, 69, 17]
Two smallest: 14 + 17 = 31
List: [81, 243, 25, 49, 123, 69, 31]
Two smallest: 25 + 31 = 56
List: [81, 243, 49, 123, 69, 56]
Two smallest: 49 + 56 = 105
List: [81, 243, 123, 69, 105]
Two smallest: 69 + 81 = 150
List: [243, 123, 105, 150]
Two smallest: 105 + 123 = 228
List: [243, 150, 228]
Two smallest: 150 + 228 = 378
List: [243, 378]
Two smallest: 243 + 378 = 621
Last item is 621.

XPL0

<lang XPL0>int List, End, Sum, Item, Smallest, I, SI; [List:= [6, 81, 243, 14, 25, 49, 123, 69, 11]; End:= 8; \last index loop [for I:= 0 to End do \show List

           [IntOut(0, List(I));  ChOut(0, ^ )];
       CrLf(0);
       if End = 0 then quit;           \done when only one element
       Sum:= 0;                        \find two smallest items
       for Item:= 1 to 2 do
           [Smallest:= -1>>1;
           for I:= 0 to End do
               if List(I) < Smallest then
                   [Smallest:= List(I);  SI:= I];
           Sum:= Sum + Smallest;       \add them
           for I:= SI to End-1 do      \remove them
               List(I):= List(I+1);
           End:= End-1;
           ];
       End:= End+1;                    \insert Sum at End
       List(End):= Sum;
       ];

]</lang>

Output:

6 81 243 14 25 49 123 69 11 
81 243 14 25 49 123 69 17 
81 243 25 49 123 69 31 
81 243 49 123 69 56 
81 243 123 69 105 
243 123 105 150 
243 150 228 
243 378 
621