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105 lines
2.8 KiB

<?php
[$instructions, $mine, $others] = explode("\n\n", file_get_contents('input.txt'));
// parse instructions
function parseInstructions($instructions): array
{
// for example : « class: 1-3 or 5-7 »
preg_match_all('/^([a-z ]+): (\d+)-(\d+) or (\d+)-(\d+)$/mi', $instructions, $matches);
if (count($matches) !== 6) {
echo sprintf('Regex failed : %s', var_export($matches, true));
exit;
}
$compares = [];
array_shift($matches);
for ($i = 0, $l = count($matches[0]); $i < $l; $i++) {
$compares[$matches[0][$i]] = static function ($number) use ($matches, $i) {
$comparison = ($number >= (int)$matches[1][$i] and $number <= (int)$matches[2][$i])
|| ($number >= (int)$matches[3][$i] and $number <= (int)$matches[4][$i]);
if ($comparison === true) {
return true;
}
return $number;
};
}
return $compares;
}
$compares = parseInstructions($instructions);
// check valid others
$others = explode("\n", $others);
array_shift($others);
$others = array_map(static function($other) {
return explode(',', $other);
}, $others);
// filter by valid tickets
$valid_tickets = [];
foreach ($others as $other) {
$is_valid = 0;
foreach ($other as $number) {
foreach ($compares as $compare) {
if ($compare((int)$number) === true) {
$is_valid++;
break;
}
}
}
if ($is_valid === 20) {
$valid_tickets[] = $other;
}
}
// filter columns by what they CAN'T be
$cant_be = [];
foreach ($valid_tickets as $valid_ticket) {
foreach ($valid_ticket as $row => $number) {
foreach ($compares as $name => $compare) {
if ($compare((int)$number) !== true) {
if (
!array_key_exists($row, $cant_be) ||
(array_key_exists($row, $cant_be) && !in_array($name, $cant_be[$row], true))
) {
$cant_be[$row][] = $name;
}
}
}
}
}
$columns = [];
$labels = array_keys($compares);
uasort($cant_be, static function($a, $b) {
return count($a) >= count($b) ? -1 : 1;
});
// label columns
foreach ($cant_be as $row => $labels_cant_be) {
foreach ($labels as $i => $label_cant_be) {
if (!in_array($label_cant_be, $labels_cant_be, true)) {
$columns[$row] = $label_cant_be;
unset($labels[$i]);
break;
}
}
}
ksort($columns);
// compare to mine
$mine = explode("\n", $mine);
array_shift($mine);
$mine = explode(',', current($mine));
$departure_fields = [];
foreach ($columns as $row => $column) {
if (strpos($column, 'departure') === 0) {
$departure_fields[] = $mine[$row];
}
}
echo array_product($departure_fields);