advent_of_code_2020/day_15/part_1.php
2020-12-15 10:15:27 +01:00

34 lines
698 B
PHP

<?php
$starting_numbers = explode(',', file_get_contents('input.txt'));
$numbers = array_map('intval', $starting_numbers);
$number = array_pop($numbers);
for ($i = count($starting_numbers); $i <= 2020; $i++) {
$number = newNumber($number);
}
echo $number;
function newNumber(int $number = 0)
{
global $numbers;
if (!in_array($number, $numbers, true)) {
$numbers[] = $number;
return $number;
}
$indexes = array_keys($numbers, $number);
if (count($indexes) === 1) {
$numbers[] = 0;
return 0;
}
$new_number = $indexes[count($indexes) - 1] - $indexes[count($indexes) - 2];
$numbers[] = $new_number;
return $new_number;
}