diff --git a/day15/day15.py b/day15/day15.py
new file mode 100644
index 0000000..69e4fcf
--- /dev/null
+++ b/day15/day15.py
@@ -0,0 +1,58 @@
+#!/usr/bin/env python3
+from collections import defaultdict
+from array import array
+
+
+def main(initial_suite, max_iteration):
+    iteration = 1
+    seen = defaultdict(int)
+
+    # init
+    for number in initial_suite:
+        seen[number] = iteration
+        iteration += 1
+
+    current = 0
+    while iteration < max_iteration:
+        last_seen = seen[current]
+        if last_seen == 0:
+            seen[current] = iteration
+            current = 0  # next
+        else:
+            seen[current] = iteration
+            current = iteration - last_seen  # next
+        iteration += 1
+    return current
+
+
+def main_array(initial_suite, max_iteration):
+    iteration = 1
+    seen = array('I', [0] * max_iteration)
+
+    # init
+    for number in initial_suite:
+        seen[number] = iteration
+        iteration += 1
+
+    current = 0
+    while iteration < max_iteration:
+        last_seen = seen[current]
+        if last_seen == 0:
+            seen[current] = iteration
+            current = 0  # next
+        else:
+            seen[current] = iteration
+            current = iteration - last_seen  # next
+        iteration += 1
+    return current
+
+
+
+
+if __name__ == "__main__":
+    inp = [6, 3, 15, 13, 1, 0]
+    # 423 µs ± 53.9 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)
+    print(main(inp, 2020))
+    # 13.6 s ± 2.89 s per loop (mean ± std. dev. of 7 runs, 1 loop each)
+    #print(main(inp, 30000000))
+    print(main_array(inp, 30000000))