#!/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);
}

##</code><code>##

POP:4:SHIFT:10
Best Score:10

##</code><code>##

use List::Util qw(shuffle);

my @numbers = shuffle(1 .. 1000);
print join(" ", @numbers);

my @copy = @numbers;

my $shiftscore = checkscore("shift");

@numbers = @copy;
my $popscore = checkscore("pop");

##</code><code>##

POP:4354:SHIFT:7452
Best Score:7452

real    0m0.049s
user    0m0.030s
sys     0m0.000s