Add day 15

d15.py

@@ -0,0 +1,22 @@
+#!/usr/bin/env python3
+
+from sys import argv
+
+i = [int(x) for x in open(argv[1]).read().strip().split(",")]
+
+a = {x:t+1 for t,x in enumerate(i[:-1])}
+t = len(i)
+l = i[-1]
+def f(x):
+    global l,t
+    while t < x:
+        if l in a:
+            n = t - a[l]
+        else:
+            n = 0
+        a[l] = t
+        t += 1
+        l = n
+    return l
+print(f(2020))
+print(f(30000000))

d15_input.txt

@@ -0,0 +1 @@
+0,13,16,17,1,10,6

d15_output.txt

@@ -0,0 +1,2 @@
+276
+31916