day 24

r0f1 · r0f1 · commit ca4735aaf713 · 2020-12-26T11:51:43.000+01:00
diff --git a/README.md b/README.md
@@ -25,5 +25,5 @@
 |[21](https://adventofcode.com/2020/day/21)|Allergen Assessment|[py](/day21/main.py)|
 |[22](https://adventofcode.com/2020/day/22)|Crab Combat|[py](/day22/main.py)|
 |[23](https://adventofcode.com/2020/day/23)|Crab Cups|[py](/day23/main.py)|
-|[24](https://adventofcode.com/2020/day/24)|-|-|
+|[24](https://adventofcode.com/2020/day/24)|Lobby Layout|[py](/day24/main.py)|
 |[25](https://adventofcode.com/2020/day/25)|-|-|
diff --git a/day24/main.py b/day24/main.py
@@ -0,0 +1,45 @@
+from collections import defaultdict
+
+def parse(s):
+    i = 0
+    res = []
+    while s:
+        if   s[0]   == "w":  res.append((-1,0)); s = s[1:]
+        elif s[0]   == "e":  res.append((1,0));  s = s[1:]
+        elif s[0:2] == "se": res.append((1,-1)); s = s[2:]
+        elif s[0:2] == "sw": res.append((0,-1)); s = s[2:]
+        elif s[0:2] == "ne": res.append((0,1));  s = s[2:]
+        elif s[0:2] == "nw": res.append((-1,1)); s = s[2:]
+    return res
+
+with open("input.txt") as f:
+    lines = [parse(x.strip()) for x in f]
+
+d = defaultdict(int)
+
+for line in lines:
+    xs, ys = zip(*line)
+    coords = sum(ys), sum(xs)
+    d[coords] = 1 - d[coords]
+    
+print(sum(d.values()))
+
+def apply(n, ns):
+    if n == 0:
+        if sum(ns) == 2:
+            return 1
+    else:
+        if sum(ns) == 0 or sum(ns) > 2:
+            return 0
+    return n
+
+dirs = [(1,-1),(0,-1),(-1,1),(0,1),(1,0),(-1,0)]
+for _ in range(100):
+    d2 = d.copy()
+    for row in range(-100,100):
+        for col in range(-100,100):
+            coords = (row,col)
+            d2[coords] = apply(d[coords], [d[k] for k in [(y+row, x+col) for x, y in dirs]])
+    d = d2
+
+print(sum(d.values()))
