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

use Test::More qw(no_plan);

sub series {
    # your code here.
}

my @tests = (
    [[1],                   undef],
    [[1, 1],                1],
    [[0, 0],                0],
    [[1, 2],                undef],
    [[0, 1, 2],             3],
    [[1, 0, -1],            -2],
    [[1, 2, 3],             4],
    [[1, 2, 4],             8],     # powers
    [[2, 4, 8],             16],
    [[1, 3, 9],             27],
    [[1, -1, 1, -1],        1],     # alternations
    [[-1, 1, -1, 1],        -1],
    [[1, 0, 1, 0],          1],
    [[0, 1, 0, 1],          0],
    [[1, 1, 2, 3, 5],       8],     # fibonacci
    [[0, 1, 1, 2, 3],       8],
    [[1, 2, 3, 5, 8],       13],
    [[1, 2, 6, 24, 120],    720],   # factorials
    [[1, 0, 0, 1],          undef],
    [[1, 2, 3, 1],          undef],
);

for my $t (@tests) {
    my $expected = defined $t->[1] ? $t->[1] : 'undef';
    my $result   = series(@{$t->[0]});
    $result = 'undef' unless defined $result;
    is $result, $expected, "seq " . join(', ', @{$t->[0]});
}