2017 Day 10 Part 2

2017/day10.py

@@ -1,13 +1,20 @@
+from functools import reduce
+
 with open("input/day10.txt") as f:
     size, input = 256, f.read().strip()
 
-lengths = [int(i) for i in input.split(",")]
 
-ring = list(range(size))
+def part1(size, input):
-pos = 0
+    lengths = [int(i) for i in input.split(",")]
-skip = 0
 
-for length in lengths:
+    ring = list(range(size))
+    _, _, ring = hash_round(0, 0, ring, lengths)
+
+    return ring[0] * ring[1]
+
+
+def hash_round(pos, skip, ring, lengths):
+    for length in lengths:
         assert length <= len(ring), "overlap undefined"
 
         tail = min(length, len(ring) - pos)
@@ -28,4 +35,28 @@ for length in lengths:
         pos = (pos + length + skip) % len(ring)
         skip += 1
 
-print(ring[0] * ring[1])
+    return pos, skip, ring
+
+
+def part2(size, input):
+    lengths = [ord(c) for c in input] + [17, 31, 73, 47, 23]
+
+    pos, skip = 0, 0
+    ring = list(range(size))
+    for _ in range(64):
+        pos, skip, ring = hash_round(pos, skip, ring, lengths)
+
+    dense = [0] * 16
+    for i in range(16):
+        start = 16 * i
+        block = ring[start : start + 16]
+        dense[i] = reduce(int.__xor__, block)
+
+    out = ""
+    for d in dense:
+        out += f"{d:02x}"
+    return out
+
+
+print(part1(size, input))
+print(part2(size, input))