Re: Recursion Confusion

[Anonymous Monk]

A tip from Visualizing recursion with the fib() example is to use Devel::TraceCalls

#!/usr/bin/perl --
use strict; use warnings;
use Devel::TraceCalls { Subs => [qw/ hanoi /]};
hanoi( 3, 'A', 'C', 'B', 0 );
sub hanoi 
{
   my ($n, $start, $end, $extra) = @_;
   if ($n == 1) 
   {
      print "Move disk #1 from $start to $end.\n";
   } 
   else 
   {
      hanoi($n-1, $start, $extra, $end);
      print "Move disk #$n from $start to $end.\n";
      hanoi($n-1, $extra, $end, $start);
   }
}
__END__

TRACE: main::hanoi( 3, 'A', 'C', 'B', 0 )
TRACE: +-main::hanoi( 2, 'A', 'B', 'C' )
TRACE: | +-main::hanoi( 1, 'A', 'C', 'B' )
Move disk #1 from A to C.
Move disk #2 from A to B.
TRACE: | +-main::hanoi( 1, 'C', 'B', 'A' )
Move disk #1 from C to B.
Move disk #3 from A to C.
TRACE: +-main::hanoi( 2, 'B', 'C', 'A' )
TRACE: | +-main::hanoi( 1, 'B', 'A', 'C' )
Move disk #1 from B to A.
Move disk #2 from B to C.
TRACE: | +-main::hanoi( 1, 'A', 'C', 'B' )
Move disk #1 from A to C.