September 2017 Update

Task/Generate-Chess960-starting-position/00DESCRIPTION

@@ -1,4 +1,4 @@
-'''[[wp:Chess960|Chess960]]'''   is a variant of chess created by world champion [[wp:Bobby Fisher|Bobby Fisher]].  Unlike other variants of the game, Chess960 does not require a different material, but instead relies on a random initial position, with a few constraints:
+'''[[wp:Chess960|Chess960]]'''   is a variant of chess created by world champion [[wp:Bobby Fischer|Bobby Fischer]].  Unlike other variants of the game, Chess960 does not require a different material, but instead relies on a random initial position, with a few constraints:
 
 * as in the standard chess game, all eight white pawns must be placed on the second rank.
 * White pieces must stand on the first rank as in the standard game, in random column order but with the two following constraints:

Task/Generate-Chess960-starting-position/JavaScript/generate-chess960-starting-position.js

@@ -22,5 +22,5 @@ function ch960startPos() {
   return rank;
 }
 
-// test
+// testing (10 times)
 for (var x = 1; x <= 10; x++) console.log(ch960startPos().join(" | "));

Task/Generate-Chess960-starting-position/Kotlin/generate-chess960-starting-position.kotlin

@@ -5,20 +5,24 @@ object Chess960 : Iterable<String> {
         if (e.length <= 1) {
             val s = b + e
             if (s.is_valid()) patterns += s
-        } else
-            for (i in 0..e.length - 1)
+        } else {
+            for (i in 0 until e.length) {
                 invoke(b + e[i], e.substring(0, i) + e.substring(i + 1))
+            }
+        }
     }
 
     private fun String.is_valid(): Boolean {
         val k = indexOf('K')
         return indexOf('R') < k && k < lastIndexOf('R') &&
-                indexOf('B') % 2 != lastIndexOf('B') % 2
+            indexOf('B') % 2 != lastIndexOf('B') % 2
     }
 
     private val patterns = sortedSetOf<String>()
 
-    init { invoke("", "KQRRNNBB") }
+    init {
+        invoke("", "KQRRNNBB")
+    }
 }
 
 fun main(args: Array<String>) {

Task/Generate-Chess960-starting-position/PARI-GP/generate-chess960-starting-position.pari

@@ -0,0 +1,9 @@
+chess960() =
+{
+  my (C = vector(8), i, j, r);
+
+  C[random(4) * 2 + 1] = C[random(4) * 2 + 2] = "B";
+  for (i = 1, 3, while (C[r = random(8) + 1],); C[r] = Vec("NNQ")[i]);
+  for (i = 1, 8, if (!C[i], C[i] = Vec("RKR")[j++]));
+  C
+}

Task/Generate-Chess960-starting-position/Phix/generate-chess960-starting-position.phix

@@ -0,0 +1,25 @@
+sequence solutions = {}
+--integer d = new_dict()
+
+for i=1 to factorial(8) do
+    sequence s = permute(i,"RNBQKBNR")
+--  sequence s = permute(rand(factorial(8),"RNBQKBNR")
+    integer b1 = find('B',s),
+            b2 = find('B',s,b1+1)
+    if and_bits(b2-b1,1)=1 then
+        integer k = find('K',s)
+        integer r1 = find('R',s)
+        integer r2 = find('R',s,r1+1)
+        if r1<k and k<r2 then
+            if find(s,solutions)=0 then
+--          if getd_index(s,d)=0 then
+--              setd(s,0,d)
+                solutions = append(solutions,s)
+            end if
+        end if
+    end if
+end for
+printf(1,"Found %d solutions\n",{length(solutions)})
+for i=1 to 5 do
+    ?solutions[rand(length(solutions))]
+end for

Task/Generate-Chess960-starting-position/REXX/generate-chess960-starting-position-3.rexx

@@ -14,7 +14,8 @@ Do r1=1 To 6
       poss=space(translate('12345678',' ',r1||kk||r2),0)
       Call rest
       End
-    End
+
+ End
   End
 say cnt.1 'solutions'
 Say time('E')
@@ -51,7 +52,7 @@ out:
   Do k=1 To 8
     ol=ol||pos.k
     End
-  cnt.1+=1
+  cnt.1=cnt.1+1
   If cnt.1<4 |,
      cnt.1>957 Then
     Say format(cnt.1,3) poss r1 kk r2  ol

Task/Generate-Chess960-starting-position/Scheme/generate-chess960-starting-position.ss

@@ -0,0 +1,56 @@
+(import (scheme base) (scheme write)
+        (srfi 1)    ; list library
+        (srfi 27))  ; random numbers
+
+(random-source-randomize! default-random-source)
+
+;; Random integer in [start, end)
+(define (random-between start end)
+  (let ((len (- end start 1)))
+    (if (< len 2)
+      start
+      (+ start (random-integer len)))))
+
+;; Random item in list
+(define (random-pick lst)
+  (if (= 1 (length lst))
+    (car lst)
+    (list-ref lst (random-integer (length lst)))))
+
+;; Construct a random piece placement for Chess960
+(define (random-piece-positions)
+  (define (free-indices positions) ; return list of empty slot indices
+    (let loop ((i 0)
+               (free '()))
+      (if (= 8 i)
+        free
+        (loop (+ 1 i)
+              (if (string=? "." (vector-ref positions i))
+                (cons i free)
+                free)))))
+  ;
+  (define (place-king+rooks positions)
+    (let ((king-posn (random-between 1 8)))
+      (vector-set! positions king-posn "K")
+      ; left-rook is between left-edge and king
+      (vector-set! positions (random-between 0 king-posn) "R")
+      ; right-rook is between right-edge and king
+      (vector-set! positions (random-between (+ 1 king-posn) 8) "R")))
+  ;
+  (define (place-bishops positions)
+    (let-values (((evens odds) (partition even? (free-indices positions))))
+                (vector-set! positions (random-pick evens) "B")
+                (vector-set! positions (random-pick odds) "B")))
+  ;
+  (let ((positions (make-vector 8 ".")))
+    (place-king+rooks positions)
+    (place-bishops positions)
+    ;; place the queen in a random remaining slot
+    (vector-set! positions (random-pick (free-indices positions)) "Q")
+    ;; place the two knights in the remaining slots
+    (for-each (lambda (idx) (vector-set! positions idx "N"))
+              (free-indices positions))
+
+    positions))
+
+(display "First rank: ") (display (random-piece-positions)) (newline)

Task/Generate-Chess960-starting-position/Zkl/generate-chess960-starting-position-1.zkl

@@ -0,0 +1,8 @@
+const pieces="KQRrBbNN";
+starts:=pieces:Utils.Helpers.permuteW(_).filter(fcn(p){
+   I:=p.index;
+   I("B") % 2 != I("b") % 2 and // Bishop constraint.
+   // King constraint.
+   ((I("r") < I("K") and I("K") < I("R")) or
+    (I("R") < I("K") and I("K") < I("r")))
+}).pump(List,"concat","toUpper"):Utils.Helpers.listUnique(_);

Task/Generate-Chess960-starting-position/Zkl/generate-chess960-starting-position-2.zkl

@@ -0,0 +1,4 @@
+N:=starts.len(); println(N);
+glyphs:=Dictionary("K","\u2654", "Q","\u2655", "R","\u2656", "B","\u2657", "N","\u2658");
+// pick some random starts and transform BBNRKQRN to glyphs
+do(10){ starts[(0).random(N)].apply(glyphs.find).println() }