my @board;
my $inversions = 1;
while ($inversions % 2) {
    @board = (0, shuffle(1..15));
    $inversions = 0;
    for my $x (1 .. 15) {
        for my $y ($x + 1 .. 15) {
            $inversions++ if $board[$x] > $board[$y];
        }
    }
}