✨ Finit le jour 2 et commence le 1 et le 3

day_2/part_1.php

@@ -0,0 +1,28 @@
+<?php
+
+$intervals = array_map(fn($interval) => explode('-', $interval), explode(',', file_get_contents('./input.txt')));
+
+$invalids = [];
+
+foreach ($intervals as $interval) {
+    [$start, $end] = $interval;
+    $current = $start;
+    while ($current <= $end) {
+        if (is_invalid($current)) {
+            $invalids[] = $current;
+        }
+
+        $current++;
+    }
+}
+
+function is_invalid($current): bool {
+    if (strlen($current) % 2 !== 0) {
+        return false;
+    }
+
+    $middle = strlen($current) / 2;
+    return substr($current, 0, $middle) === substr($current, $middle);
+}
+
+echo array_sum($invalids);