Day 24

day24/part2.py

@@ -0,0 +1,51 @@
+#!/usr/bin/env python3
+import numpy as np
+from scipy.signal import convolve
+
+lines = (x.strip() for x in open("input.txt"))
+
+blacks = set()
+
+for line in lines:
+    x, y = 0, 0
+    while len(line):
+        if line[0] == "n":
+            y += 1
+            x += 1 if line[1] == "e" else 0
+            line = line[2:]
+        elif line[0] == "s":
+            y -= 1
+            x -= 1 if line[1] == "w" else 0
+            line = line[2:]
+        else:
+            x += 1 if line[0] == "e" else -1
+            line = line[1:]
+    if (x, y) in blacks:
+        blacks.discard((x, y))
+    else:
+        blacks.add((x, y))
+
+
+x = np.array(list([x, y] for x, y in blacks)).T
+lower = np.min(x, axis=1)
+upper = np.max(x, axis=1)
+grid = np.zeros((upper[0]-lower[0]+1, upper[1]-lower[1]+1))
+x -= np.array([lower]).T
+grid[x[0], x[1]] = 1
+kernel = np.array([
+    [1, 1, 0],
+    [1, 0, 1],
+    [0, 1, 1]
+])
+
+for _ in range(100):
+    grid = np.pad(grid, pad_width=1)
+    neighbors = convolve(grid, kernel, mode='same', method="direct")
+    set_inactive = np.logical_and(grid == 1, np.logical_or(neighbors == 0, neighbors > 2))
+    set_active = np.logical_and(grid == 0, neighbors == 2)
+    grid[set_inactive] = 0
+    grid[set_active] = 1
+    a = tuple(slice(np.min(idxs), np.max(idxs)+1) for idxs in np.where(grid == 1))
+    grid = grid[a]
+
+print(np.sum(grid))