use strict;
use warnings;

sub verify_correctness
{
    my $n = shift;
    my $sched = shift;

    my $who_against_who = [ map { [ (0) x $n ] } (1 .. $n) ];

    my $day;
    for $day (0 .. ($n-2))
    {
        my $day_sched = $sched->[$day];
        for my $team (0 .. ($n-1))
        {
            my $other_team = $day_sched->[$team];
            if ($other_team == $team)
            {
                print STDERR "Day $day Team $team competes against itself.\n";
                return 1;
            }
            if (($other_team < 0) || ($other_team >= $n))
            {
                print STDERR "Day $day Team $team\'s opponent out of range.";
                return 1;
            }
            if ($day_sched->[$other_team] != $team)
            {
                print STDERR "Day $day Team $team opponent is not itself\n";
                return 1;
            }
            if (++$who_against_who->[$team]->[$other_team] > 2)
            {
                print STDERR 
                    "Teams $team, $other_team team played more than once\n";
                return 1;
            }
            if (++$who_against_who->[$other_team]->[$team] > 2)
            {
                print STDERR 
                    "Teams $team, $other_team team played more than once\n";
                return 1;
            }
        }
    }
    for my $team (0 .. ($n-1))
    {
        for my $other_team (0 .. ($n-1))
        {
            if ($who_against_who->[$team]->[$other_team] != 
                (($team == $other_team) ? 0 : 2))
            {
                print STDERR "w_a_w[$team][$other_team] is wrong.\n";
                return 1;
            }
        }
    }
    return 0;
}

1;