diff --git a/day_15/part_1.php b/day_15/part_1.php
new file mode 100644
index 0000000..6394c21
--- /dev/null
+++ b/day_15/part_1.php
@@ -0,0 +1,33 @@
+<?php
+
+$starting_numbers = explode(',', file_get_contents('input.txt'));
+
+$numbers = array_map('intval', $starting_numbers);
+$number = array_pop($numbers);
+for ($i = count($starting_numbers); $i <= 2020; $i++) {
+    $number = newNumber($number);
+}
+
+echo $number;
+
+function newNumber(int $number = 0)
+{
+    global $numbers;
+    if (!in_array($number, $numbers, true)) {
+        $numbers[] = $number;
+
+        return $number;
+    }
+
+    $indexes = array_keys($numbers, $number);
+
+    if (count($indexes) === 1) {
+        $numbers[] = 0;
+        return 0;
+    }
+
+    $new_number = $indexes[count($indexes) - 1] - $indexes[count($indexes) - 2];
+    $numbers[] = $new_number;
+
+    return $new_number;
+}
diff --git a/day_15/part_2.php b/day_15/part_2.php
new file mode 100644
index 0000000..c64084a
--- /dev/null
+++ b/day_15/part_2.php
@@ -0,0 +1,39 @@
+<?php
+
+$starting_numbers = explode(',', file_get_contents('input.txt'));
+
+$tmp_numbers = array_map('intval', $starting_numbers);
+$count_numbers = [];
+foreach ($tmp_numbers as $i => $tmp_number) {
+    if (array_key_exists($tmp_number, $count_numbers)) {
+        $count_numbers[$tmp_number][] = $i;
+    } else {
+        $count_numbers[$tmp_number] = [$i];
+    }
+}
+$number = end($tmp_numbers);
+unset($tmp_numbers, $tmp_number);
+
+for ($i = count($starting_numbers); $i <= 29999999; $i++) {
+    $number = newNumber($i, $number);
+}
+
+echo $number;
+
+function newNumber(int $i, int $number = 0)
+{
+    global $count_numbers;
+    if (!array_key_exists($number, $count_numbers)) {
+        $count_numbers[$number] = [$i];
+
+        return $number;
+    }
+
+    $count_indexes = count($count_numbers[$number]);
+
+    $new_number = $count_indexes === 1 ? 0 : $count_numbers[$number][$count_indexes - 1] - $count_numbers[$number][$count_indexes - 2];
+
+    $count_numbers[$new_number][] = $i;
+
+    return $new_number;
+}