Day 15

2020/day15.py

@@ -0,0 +1,32 @@
+import sys
+from collections import defaultdict
+
+
+def main():
+    nl = list(map(lambda s: int(s), sys.stdin.read().rstrip().split(",")))
+
+    # Part 1
+    print("Part 1:", get_nth(2020, nl))
+    # Part 2
+    print("Part 2:", get_nth(30000000, nl))
+
+
+def get_nth(limit, starters):  # pretty horrible complexity but i'm behind sched
+    said = defaultdict(list)
+    for turn in range(1, limit + 1):
+        if turn <= len(starters):  # starting number shit special case.
+            n = starters[turn - 1]
+        else:
+            last_spoken = n
+            if len(said[last_spoken]) == 1:
+                n = 0
+            else:
+                last_turn_said = said[last_spoken][-2]
+                n = turn - 1 - last_turn_said
+        said[n].append(turn)
+        said[n] = said[n][-2:]
+    return n
+
+
+if __name__ == "__main__":
+    main()