Day 09

day09/part2.py

@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+import numpy as np
+
+lines = (x.strip() for x in open("input.txt"))
+positions = set()
+rope = [np.array((0, 0)) for _ in range(10)]
+dirs = {d: p for d, p in zip("UDLR", ((1, 0), (-1, 0), (0, -1), (0, 1)))}
+
+for line in lines:
+    d, n = dirs[line[0]], int(line[2:])
+    for _ in range(n):
+        rope[0] += d
+        for i in range(1, len(rope)):
+            diff = rope[i-1] - rope[i]
+            rope[i] += np.sign(diff) if sum(np.abs(diff)) > 2 else np.sign(diff - np.sign(diff))
+        positions.add(tuple(rope[len(rope)-1]))
+
+print(len(positions))