✨ Finit le jour 9

day_9/part_1.php

@@ -0,0 +1,22 @@
+<?php
+
+$numbers = array_map('intval', explode("\n", file_get_contents('input.txt')));
+
+$current_index = 0;
+
+$step = 25;
+
+while (true) {
+    for ($l = count($numbers) - $step; $current_index <= $l; $current_index++) {
+        $number_to_test = $numbers[$current_index + $step];
+        $numbers_to_addition = array_slice($numbers, $current_index, $step);
+        foreach ($numbers_to_addition as $number) {
+            if (in_array($number_to_test - $number, $numbers_to_addition, true)) {
+                $current_index++;
+                break 2;
+            }
+        }
+        echo $number_to_test;
+        exit;
+    }
+}