sub fannkuch { my ( $copy, $level, $split ) = ( @_, 0, 1 ); my ( $index, $next ) = ( $level, $level + 1 ); my $length = length($copy); if ($next == $length) { ($index, $split) = ($split - 1, $level); substr($copy, $index, 0) = chop($copy); } do { if ($next == $length) { unless ( ord($copy) == $length and $level < $maxflips ) { my $q = $copy; my ( $k, $flips ); for ( $flips = 0; ( $k = ord( $q ) ) != 1; $flips++ ) { substr( $q, 0, $k ) = reverse substr( $q, 0, $k ); } if ( $flips >= $maxflips ) { if ( $flips == $maxflips) { push @max_sequence, $copy; } else { $maxflips = $flips; @max_sequence = ($copy); } } } } else { fannkuch( $copy, $next, $split ); } substr( $copy, $index - 1, 2 ) = reverse substr( $copy, $index - 1, 2 ); $split = $next if $index == $split; } while $index--; return $maxflips; }