Data commit

Task/Permutations/Raku/permutations-1.raku

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+.say for <a b c>.permutations

Task/Permutations/Raku/permutations-2.raku

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+sub next_perm ( @a is copy ) {
+    my $j = @a.end - 1;
+    return Nil if --$j < 0 while @a[$j] after @a[$j+1];
+
+    my $aj = @a[$j];
+    my $k  = @a.end;
+    $k-- while $aj after @a[$k];
+    @a[ $j, $k ] .= reverse;
+
+    my $r = @a.end;
+    my $s = $j + 1;
+    @a[ $r--, $s++ ] .= reverse while $r > $s;
+    return @a;
+}
+
+.say for [<a b c>], &next_perm ...^ !*;

Task/Permutations/Raku/permutations-3.raku

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+sub permute(+@items) {
+   my @seq := 1..+@items;
+   gather for (^[*] @seq) -> $n is copy {
+      my @order;
+      for @seq {
+         unshift @order, $n mod $_;
+         $n div= $_;
+      }
+      my @i-copy = @items;
+      take map { |@i-copy.splice($_, 1) }, @order;
+   }
+}
+.say for permute( 'a'..'c' )

Task/Permutations/Raku/permutations-4.raku

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+.say for permutations(3);

Task/Permutations/Raku/permutations-5.raku

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+# Heap’s algorithm for generating permutations. Algorithm 2 in
+# Robert Sedgewick, 1977. Permutation generation methods. ACM
+# Comput. Surv. 9, 2 (June 1977), 137-164.
+
+define(n, 3)
+define(n_minus_1, 2)
+
+implicit none
+
+integer a(1:n)
+
+integer c(1:n)
+integer i, k
+integer tmp
+
+10000 format ('(', I1, n_minus_1(' ', I1), ')')
+
+# Initialize the data to be permuted.
+do i = 1, n {
+   a(i) = i
+}
+
+# What follows is a non-recursive Heap’s algorithm as presented by
+# Sedgewick. Sedgewick neglects to fully initialize c, so I have
+# corrected for that. Also I compute k without branching, by instead
+# doing a little arithmetic.
+do i = 1, n {
+   c(i) = 1
+}
+i = 2
+write (*, 10000) a
+while (i <= n) {
+   if (c(i) < i) {
+      k = mod (i, 2) + ((1 - mod (i, 2)) * c(i))
+      tmp = a(i)
+      a(i) = a(k)
+      a(k) = tmp
+      c(i) = c(i) + 1
+      i = 2
+      write (*, 10000) a
+   } else {
+      c(i) = 1
+      i = i + 1
+   }
+}
+
+end

Task/Permutations/Raku/permutations-6.raku

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+C Output from Public domain Ratfor, version 1.0
+      implicit none
+      integer a(1: 3)
+      integer c(1: 3)
+      integer i, k
+      integer tmp
+10000 format ('(', i1,  2(' ', i1), ')')
+      do23000 i = 1,  3
+      a(i) = i
+23000 continue
+23001 continue
+      do23002 i = 1,  3
+      c(i) = 1
+23002 continue
+23003 continue
+      i = 2
+      write (*, 10000) a
+23004 if(i .le.  3)then
+      if(c(i) .lt. i)then
+      k = mod (i, 2) + ((1 - mod (i, 2)) * c(i))
+      tmp = a(i)
+      a(i) = a(k)
+      a(k) = tmp
+      c(i) = c(i) + 1
+      i = 2
+      write (*, 10000) a
+      else
+      c(i) = 1
+      i = i + 1
+      endif
+      goto 23004
+      endif
+23005 continue
+      end