Solve day 18

18_lumber.py

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+#!/usr/bin/env python3
+import sys
+import time
+
+OPEN, TREE, LUMB = range(3)
+
+trans = {'.': OPEN, '|': TREE, '#': LUMB}
+initial = []
+for line in sys.stdin:
+    w = len(line) + 1
+    initial += [OPEN, *(trans[c] for c in line.rstrip()), OPEN]
+pad = [OPEN] * w
+initial = pad + initial + pad
+h = len(initial) // w
+
+def simulate(minutes):
+    prev = list(initial)
+    grid = [0] * len(prev)
+
+    for minute in range(minutes):
+        for y in range(1, h - 1):
+            for x in range(1, w - 1):
+                i = y * w + x
+                cell = prev[i]
+
+                counts = [0, 0, 0]
+                for d in (-w - 1, -w, -w + 1, -1, 1, w - 1, w, w + 1):
+                    counts[prev[i + d]] += 1
+
+                if cell == OPEN and counts[TREE] >= 3:
+                    cell = TREE
+                elif cell == TREE and counts[LUMB] >= 3:
+                    cell = LUMB
+                elif cell == LUMB and (not counts[LUMB] or not counts[TREE]):
+                    cell = OPEN
+
+                grid[i] = cell
+
+        counts = [0, 0, 0]
+        for x in grid:
+            counts[x] += 1
+        yield counts[TREE] * counts[LUMB], hash(tuple(grid))
+
+        prev, grid = grid, prev
+
+# part 1
+for val, ident in simulate(10):
+    last = val
+print(last)
+
+# part 2
+def find_pattern(n):
+    seen = []
+    for minute, result in enumerate(simulate(n)):
+        for i in range(len(seen) - 1, -1, -1):
+            if seen[i] == result:
+                return minute, tuple(zip(*seen[i:]))[0]
+        seen.append(result)
+
+n = 1000000000
+minute, pattern = find_pattern(n)
+print(pattern[(n - minute - 1) % len(pattern)])

input/18

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