Day 21

day20/part1-v2.py

@@ -0,0 +1,53 @@
+#!/usr/bin/env python3
+
+from collections import defaultdict
+from functools import reduce
+
+import numpy as np
+
+
+lines = (x.strip() for x in open("input.txt"))
+rotations = [(t, r) for t in (True, False) for r in range(4)]
+tiles = {}
+borders = defaultdict(set)
+
+
+def add_tile(num, tile):
+    global tiles, borders
+    tiles[num] = tile
+    for transpose, rotate in rotations:
+        view = np.rot90(tile.T if transpose else tile, rotate)
+        edge = np.packbits(view[0])
+        edge = edge[0] * 4 + edge[1] // 64
+        borders[edge].add(num)
+
+
+for line in lines:
+    if line.startswith("Tile"):
+        num = int(line[5:-1])
+        tile = np.zeros((10, 10), dtype=np.int16)
+        lnr = 0
+    elif line == "":
+        add_tile(num, tile)
+    else:
+        a = np.array([(0 if x == '.' else 1) for x in line], dtype=np.int16)
+        tile[lnr] = a
+        lnr += 1
+add_tile(num, tile)
+
+# every border matches only once
+print("sum    joints", sum(1 for key, val in borders.items() if len(val) > 1))
+print("should joints", (len(tiles)-np.sqrt(len(tiles))) * 2)
+print("sum    outer", sum(1 for key, val in borders.items() if len(val) == 1))
+print("should outer", np.sqrt(len(tiles)) * 4)
+print("cnt tiles", len(tiles))
+print("multi matches", sum(1 for key, val in borders.items() if len(val) > 2))
+
+# find corners
+edges = defaultdict(int)
+for key, val in borders.items():
+    if len(val) == 1:
+        for item in val:
+            edges[item] += 1
+
+print(reduce(lambda a, b: a*b, (key for key, val in edges.items() if val == 4), 1))