✨ Finit le jour 5

day_5/part_1.php

@@ -0,0 +1,48 @@
+<?php
+
+$ids = explode("\n", file_get_contents('input.txt'));
+//$ids = ['FBFBBFFRLR'];
+
+$max_seat_id = 0;
+
+function decodeRow($row)
+{
+    $min = 1;
+    $max = 128;
+
+    foreach (str_split($row) as $cell) {
+        if ($cell === 'F') {
+            $max = floor($min + ($max - $min) / 2);
+        } else {
+            $min = ceil($max - ($max - $min) / 2);
+        }
+    }
+
+    return $min - 1;
+}
+
+function decodeColumn($column)
+{
+    $min = 1;
+    $max = 8;
+
+    foreach (str_split($column) as $cell) {
+        if ($cell === 'L') {
+            $max = floor($min + ($max - $min) / 2);
+        } else {
+            $min = ceil($max - ($max - $min) / 2);
+        }
+    }
+
+    return $min - 1;
+}
+
+foreach ($ids as $id) {
+    $encoded_row = substr($id, 0, 7);
+    $encoded_column = substr($id, 7);
+    $row = decodeRow($encoded_row);
+    $column = decodeColumn($encoded_column);
+    $max_seat_id = max($max_seat_id, ($row * 8 + $column));
+}
+
+echo $max_seat_id;