advent_of_code_2020/day_6/part_1.php

<?php

$groups = explode("\n\n", file_get_contents('input.txt'));

$yesses = 0;

foreach ($groups as $group) {
    $group_yes = implode('', explode("\n", $group));
    $yesses += count(array_unique(str_split($group_yes)));
}

echo $yesses;