Add day 23.

2022/day23.py

@@ -1,3 +1,105 @@
 # -*- encoding: utf-8 -*-
 
+import itertools
 import sys
+from collections import defaultdict
+
+Directions = list[
+    tuple[
+        str, tuple[int, int], tuple[tuple[int, int], tuple[int, int], tuple[int, int]]
+    ]
+]
+
+# (Y, X)
+DIRECTIONS: Directions = [
+    ("N", (-1, 0), ((-1, -1), (-1, 0), (-1, 1))),
+    ("S", (1, 0), ((1, -1), (1, 0), (1, 1))),
+    ("W", (0, -1), ((-1, -1), (0, -1), (1, -1))),
+    ("E", (0, 1), ((-1, 1), (0, 1), (1, 1))),
+]
+
+
+def min_max_yx(positions: set[tuple[int, int]]) -> tuple[int, int, int, int]:
+    ys, xs = {y for y, x in positions}, {x for y, x in positions}
+    return min(ys), min(xs), max(ys), max(xs)
+
+
+def print_positions(positions: set[tuple[int, int]]):
+    min_y, min_x, max_y, max_x = min_max_yx(positions)
+    print(
+        "\n".join(
+            "".join(
+                "#" if (y, x) in positions else "." for x in range(min_x - 1, max_x + 2)
+            )
+            for y in range(min_y - 1, max_y + 2)
+        )
+    )
+
+
+def round(
+    positions: set[tuple[int, int]],
+    directions: Directions,
+):
+    to_move: dict[tuple[int, int], list[tuple[int, int]]] = defaultdict(lambda: [])
+    for (y, x) in positions:
+        elves = {
+            (dy, dx): (y + dy, x + dx) in positions
+            for dy, dx in itertools.product((-1, 0, 1), (-1, 0, 1))
+            if (dy, dx) != (0, 0)
+        }
+
+        if not any(elves.values()):
+            to_move[y, x].append((y, x))
+            continue
+
+        found: str | None = None
+        for d, (dy, dx), d_yx_check in directions:
+            if not any(elves[dy, dx] for dy, dx in d_yx_check):
+                found = d
+                to_move[y + dy, x + dx].append((y, x))
+                break
+        if found is None:
+            to_move[y, x].append((y, x))
+
+    positions.clear()
+    for ty, tx in to_move:
+        if len(to_move[ty, tx]) > 1:
+            positions.update(to_move[ty, tx])
+        else:
+            positions.add((ty, tx))
+
+    directions.append(directions.pop(0))
+
+
+POSITIONS = {
+    (i, j)
+    for i, row in enumerate(sys.stdin.read().splitlines())
+    for j, col in enumerate(row)
+    if col == "#"
+}
+
+# === part 1 ===
+
+p1, d1 = POSITIONS.copy(), DIRECTIONS.copy()
+for r in range(10):
+    round(p1, d1)
+
+min_y, min_x, max_y, max_x = min_max_yx(p1)
+answer_1 = sum(
+    (y, x) not in p1 for y in range(min_y, max_y + 1) for x in range(min_x, max_x + 1)
+)
+print(f"answer 1 is {answer_1}")
+
+# === part 2 ===
+
+p2, d2 = POSITIONS.copy(), DIRECTIONS.copy()
+answer_2 = 0
+while True:
+    answer_2 += 1
+    backup = p2.copy()
+    round(p2, d2)
+
+    if backup == p2:
+        break
+
+print(f"answer 2 is {answer_2}")

2022/inputs/day23.txt

@@ -0,0 +1,70 @@
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2022/tests/day23.txt

@@ -0,0 +1,7 @@
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+.#..#..