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

my @numbers = qw(16 2 10 2 9 17 5 8 15 14 20 19 19 11 10 11 9 13 7 13);
my $shiftscore = checkscore("shift");

@numbers = qw(16 2 10 2 9 17 5 8 15 14 20 19 19 11 10 11 9 13 7 13);
my $popscore = checkscore("pop");

my $bestscore = $popscore > $shiftscore
    ? $popscore
    : $shiftscore;

print "POP:$popscore:SHIFT:$shiftscore";
print "Best Score:$bestscore";

sub checkscore {
    my $first_turn = shift;
    my ($player, $opponent);
    $player = $first_turn eq "pop"
        ? pop(@numbers)
        : shift(@numbers);
    while (@numbers) {
        $opponent += $numbers[0] > $numbers[-1]
            ? shift(@numbers)
            : pop(@numbers);
        last if !@numbers;
        $player += $numbers[0] > $numbers[-1]
            ? shift(@numbers)
            : pop(@numbers);
    }
    return ($player - $opponent);
}