my @output;
printDiff($#s1, $#s2);
print join "\n", @output;

sub printDiff {
        my ($i, $j) = @_;
        if ($i > 0 && $j > 0 and $s1[$i] eq $s2[$j]) {
                printDiff($i-1, $j-1);
                $output[0] .= "  " . $s1[$i];
                $output[1] .= "  " . $s1[$i];
        }
        else {
                if ($j > 0 && ($i == 0 || $M[$i][$j-1] >= $M[$i-1][$j])) {
                        printDiff($i, $j-1);
                        $output[1] .= " <" . $s2[$j] . ">";
                }
                elsif ($i > 0 && ($j == 0 || $M[$i][$j-1] < $M[$i-1][$j])) {
                        printDiff($i-1, $j);
                        $output[0] .= " [" . $s1[$i] . "]";
                }
        }
}