diff --git a/day_5/part_1.php b/day_5/part_1.php
new file mode 100644
index 0000000..a207ae3
--- /dev/null
+++ b/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 $max_seat_id;
\ No newline at end of file
diff --git a/day_5/part_2.php b/day_5/part_2.php
new file mode 100644
index 0000000..3346a54
--- /dev/null
+++ b/day_5/part_2.php
@@ -0,0 +1,53 @@
+<?php
+
+$ids = explode("\n", file_get_contents('input.txt'));
+//$ids = ['FBFBBFFRLR'];
+
+$seat_ids = [];
+
+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);
+    $seat_ids[] = $row * 8 + $column;
+}
+
+sort($seat_ids);
+for ($i = current($seat_ids), $l = end($seat_ids), reset($seat_ids); $i <= $l; $i++) {
+    if (!in_array($i, $seat_ids, true)) {
+        echo $i;
+    }
+}
\ No newline at end of file