Data commit

Task/Topswops/Perl/topswops.pl

@@ -0,0 +1,35 @@
+sub next_swop {
+  my( $max, $level, $p, $d ) = @_;
+  my $swopped = 0;
+  for( 2..@$p ){ # find possibilities
+    my @now = @$p;
+    if( $_ == $now[$_-1] ) {
+      splice @now, 0, 0, reverse splice @now, 0, $_;
+      $swopped = 1;
+      next_swop( $max, $level+1, \@now, [ @$d ] );
+    }
+  }
+  for( 1..@$d ) { # create possibilities
+    my @now = @$p;
+    my $next = shift @$d;
+    if( not $now[$next-1] ) {
+      $now[$next-1] = $next;
+      splice @now, 0, 0, reverse splice @now, 0, $next;
+      $swopped = 1;
+      next_swop( $max, $level+1, \@now, [ @$d ] );
+    }
+    push @$d, $next;
+  }
+  $$max = $level if !$swopped and $level > $$max;
+}
+
+sub topswops {
+  my $n = shift;
+  my @d = 2..$n;
+  my @p = ( 1, (0) x ($n-1) );
+  my $max = 0;
+  next_swop( \$max, 0, \@p, \@d );
+  return $max;
+}
+
+printf "Maximum swops for %2d cards: %2d\n", $_, topswops $_ for 1..10;