#!/usr/bin/perl -w
use strict;

my $recursion = 0;

sub hanoi {
   my ($n, $start, $end, $extra) = @_;
   $recursion++;
   my $indent = "  " x $recursion;

   print $indent, "Entering hanoi($n, $start, $end, $extra)\n";

   if ($n == 1) {
       print $indent, "Move disk #1 from $start to $end.\n";
   } else {
        hanoi($n-1, $start, $extra, $end);
        print $indent, "Move disk #$n from $start to $end.\n";
        hanoi($n-1, $extra, $end, $start);
   }
   print $indent, "Leaving hanoi($n, $start, $end, $extra)\n";
   $recursion--;
}

hanoi(3, 'A', 'C', 'B');
__END__
  Entering hanoi(3, A, C, B)
    Entering hanoi(2, A, B, C)
      Entering hanoi(1, A, C, B)
      Move disk #1 from A to C.
      Leaving hanoi(1, A, C, B)
    Move disk #2 from A to B.
      Entering hanoi(1, C, B, A)
      Move disk #1 from C to B.
      Leaving hanoi(1, C, B, A)
    Leaving hanoi(2, A, B, C)
  Move disk #3 from A to C.
    Entering hanoi(2, B, C, A)
      Entering hanoi(1, B, A, C)
      Move disk #1 from B to A.
      Leaving hanoi(1, B, A, C)
    Move disk #2 from B to C.
      Entering hanoi(1, A, C, B)
      Move disk #1 from A to C.
      Leaving hanoi(1, A, C, B)
    Leaving hanoi(2, B, C, A)
  Leaving hanoi(3, A, C, B)