2020/11

y2020/p11.py

@@ -0,0 +1,42 @@
+import itertools
+import sys
+
+import toolkit
+
+
+def is_taken(pos, state):
+    taken = sum(pos + step in state for step in moves)
+    if pos not in state and not taken:
+        return True
+    elif pos in state and taken >= 4:
+        return False
+    return pos in state
+
+
+def is_taken2(pos, state):
+    taken = 0
+    for step in moves:
+        for x in itertools.count(1):
+            adj = (pos + step * x)
+            if adj in seats or adj not in grid:
+                taken += adj in state
+                break
+    if pos not in state and not taken:
+        return True
+    elif pos in state and taken >= 5:
+        return False
+    return pos in state
+
+
+text = sys.stdin.read()
+grid, _, _ = toolkit.read_image(text)
+moves = {dx + dy for dx in [-1, 0, 1] for dy in [-1j, 0, 1j]} - {0}
+seats = {pos for pos, value in grid.items() if value != '.'}
+
+for fn in [is_taken, is_taken2]:
+    state = frozenset()
+    seen = set()
+    while state not in seen:
+        seen.add(state)
+        state = frozenset({pos for pos in seats if fn(pos, state)})
+    print(len(state))