From aa26b736440b8a8290bc45f2e396428ea1cd220f Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Fri, 23 Dec 2022 10:00:35 +0100
Subject: [PATCH] 2022: d23: ex2: add solution

---
 2022/d23/ex2/ex2.py | 102 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 102 insertions(+)
 create mode 100755 2022/d23/ex2/ex2.py

diff --git a/2022/d23/ex2/ex2.py b/2022/d23/ex2/ex2.py
new file mode 100755
index 0000000..26eae2e
--- /dev/null
+++ b/2022/d23/ex2/ex2.py
@@ -0,0 +1,102 @@
+#!/usr/bin/env python
+
+import itertools
+import sys
+from collections import defaultdict, deque
+from collections.abc import Iterator, Sequence
+from typing import NamedTuple
+
+
+class Point(NamedTuple):
+    x: int
+    y: int
+
+    def __add__(self, other):
+        if not isinstance(other, Point):
+            return NotImplemented
+        return Point(self.x + other.x, self.y + other.y)
+
+    def __sub__(self, other):
+        if not isinstance(other, Point):
+            return NotImplemented
+        return Point(self.x - other.x, self.y - other.y)
+
+
+ElfMap = set[Point]
+
+
+def neighbours(p: Point) -> Iterator[Point]:
+    for dx, dy in itertools.product(range(-1, 1 + 1), repeat=2):
+        if dx == 0 and dy == 0:
+            continue
+        yield p + Point(dx, dy)
+
+
+class MoveCandidate(NamedTuple):
+    dir: Point
+    empties: set[Point]
+
+
+MOVES = [
+    # North
+    MoveCandidate(Point(-1, 0), {Point(-1, -1), Point(-1, 0), Point(-1, 1)}),
+    # South
+    MoveCandidate(Point(1, 0), {Point(1, -1), Point(1, 0), Point(1, 1)}),
+    # West
+    MoveCandidate(Point(0, -1), {Point(-1, -1), Point(0, -1), Point(1, -1)}),
+    # East
+    MoveCandidate(Point(0, 1), {Point(-1, 1), Point(0, 1), Point(1, 1)}),
+]
+
+
+def solve(input: list[str]) -> int:
+    def to_map(input: list[str]) -> ElfMap:
+        res: ElfMap = set()
+        for x, line in enumerate(input):
+            for y, c in enumerate(line):
+                if c != "#":
+                    continue
+                res.add(Point(x, y))
+        return res
+
+    def do_round(map: ElfMap, moves: Sequence[MoveCandidate]) -> ElfMap:
+        move: dict[Point, Point] = {elf: elf for elf in map}
+        dest_count: dict[Point, int] = defaultdict(int)
+        # Consider destinations all at once
+        for elf in map:
+            if not any(n in map for n in neighbours(elf)):
+                continue
+            for candidate in iter(moves):
+                if any((elf + delta) in map for delta in candidate.empties):
+                    continue
+                dest = elf + candidate.dir
+                move[elf] = dest
+                dest_count[dest] += 1
+                break
+        # Only move elves that don't overlap
+        res: ElfMap = set()
+        for elf, dest in move.items():
+            if dest_count[dest] > 1:
+                res.add(elf)
+            else:
+                res.add(dest)
+        assert len(res) == len(map)  # Sanity check
+        return res
+
+    map = to_map(input)
+    moves = deque(MOVES)
+    i = 1
+    while (new_map := do_round(map, moves)) != map:
+        map = new_map
+        moves.rotate(-1)
+        i += 1
+    return i
+
+
+def main() -> None:
+    input = sys.stdin.read().splitlines()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()