3rd and 2nd day

03/part1.php

@@ -0,0 +1,19 @@
+<?php
+
+$input = file('input', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
+$input = array_map(fn($line) => str_split($line), $input);
+
+$o2 = $co2 = $input;
+
+for ($i = 0; $i < count($input[0]); $i++) {
+    if (count($o2) > 1) {
+        $bit = (int)(array_sum($column = array_column($o2, $i)) >= ceil(count($column) / 2));
+        $o2 = array_filter($o2, fn($line) => $line[$i] == $bit);
+    }
+
+    if (count($co2) > 1) {
+        $bit = (int) (array_sum($column = array_column($co2, $i)) >= ceil(count($column) / 2));
+        $co2 = array_filter($co2, fn ($line) => $line[$i] != $bit);
+    }
+}
+echo bindec(implode('', reset($co2))) * bindec(implode('', reset($o2)));