#!/usr/bin/perl
use warnings;
use strict;

sub triangle_sum {
    my ($triangle) = @_;
    my @sums = @{ $triangle->[-1] };
    @sums = map {
        $sums[$sums[ $_ - 1 ] < $sums[$_] ? $_ - 1 : $_]
            + $triangle->[@sums - 2][ $_ - 1 ]
        } 1 .. $#sums
        while @sums > 1;
    return $sums[0]
}

use Test::More;

is triangle_sum ([ [1], [2,4], [6,4,9], [5,1,7,2] ]), 8, 'Example 1';
is triangle_sum ([ [3], [3,1], [5,2,3], [4,3,1,3] ]), 7, 'Example 2';

is triangle_sum([[2], [1, 5], [9, 10, 1]]), 8, 'Tricky';

done_testing();