✨ Finit le jour 4

day_4/part_1.php

@@ -0,0 +1,17 @@
+<?php
+
+$elves = explode("\n", file_get_contents('./input.txt'));
+
+echo count(
+    array_filter(
+        $elves,
+        static function($elf) {
+            [$section1, $section2] = array_map(static fn($section) => explode('-', $section), explode(',', $elf));
+            return
+                ($section2[0] >= $section1[0] && $section2[1] <= $section1[1])
+                ||
+                ($section1[0] >= $section2[0] && $section1[1] <= $section2[1])
+                ;
+        }
+    )
+);

day_4/part_2.php

@@ -0,0 +1,15 @@
+<?php
+
+$elves = explode("\n", file_get_contents('./input.txt'));
+
+echo count(
+    array_filter(
+        $elves,
+        static function($elf) {
+            [$section1, $section2] = array_map(static fn($section) => explode('-', $section), explode(',', $elf));
+            return count(
+                array_intersect(range($section1[0], $section1[1]), range($section2[0], $section2[1]))
+            ) > 0;
+        }
+    )
+);