2022: d18: ex2: add solution

2022/d18/ex2/ex2.py

@@ -0,0 +1,119 @@
+#!/usr/bin/env python
+
+import itertools
+import sys
+from collections import deque
+from collections.abc import Iterator
+from typing import NamedTuple
+
+
+class Point3(NamedTuple):
+    x: int
+    y: int
+    z: int
+
+    @classmethod
+    def from_input(cls, input: str) -> "Point3":
+        x, y, z = map(int, input.split(","))
+        return cls(x, y, z)
+
+    @classmethod
+    def neighbours(cls, p: "Point3") -> Iterator["Point3"]:
+        for dx, dy, dz in (
+            (0, 0, -1),
+            (0, 0, 1),
+            (0, -1, 0),
+            (0, 1, 0),
+            (-1, 0, 0),
+            (1, 0, 0),
+        ):
+            yield cls(p.x + dx, p.y + dy, p.z + dz)
+
+
+def solve(input: list[str]) -> int:
+    def compute_unreachable(cubes: set[Point3]) -> set[Point3]:
+        def explore(p: Point3, can_reach_out: dict[Point3, bool]) -> bool:
+            seen: set[Point3] = set()
+            queue: list[Point3] = [p]
+            while queue:
+                p = queue.pop()
+                if p in seen:
+                    continue
+                if p in can_reach_out:
+                    if can_reach_out[p]:
+                        return True
+                    continue  # Don't go through walls
+                seen.add(p)
+                queue.extend(Point3.neighbours(p))
+            return False
+
+        minx, maxx = min(p.x for p in cubes), max(p.x for p in cubes)
+        miny, maxy = min(p.y for p in cubes), max(p.y for p in cubes)
+        minz, maxz = min(p.z for p in cubes), max(p.z for p in cubes)
+
+        can_reach_out = {p: False for p in cubes}
+        can_reach_out |= {
+            Point3(x, y, z): True
+            for x, (y, z) in zip(
+                itertools.repeat(minx - 1),
+                itertools.product(range(miny, maxy + 1), range(minz, maxz + 1)),
+            )
+        }
+        can_reach_out |= {
+            Point3(x, y, z): True
+            for x, (y, z) in zip(
+                itertools.repeat(maxx + 1),
+                itertools.product(range(miny, maxy + 1), range(minz, maxz + 1)),
+            )
+        }
+        can_reach_out |= {
+            Point3(x, y, z): True
+            for y, (x, z) in zip(
+                itertools.repeat(miny - 1),
+                itertools.product(range(minx, maxx + 1), range(minz, maxz + 1)),
+            )
+        }
+        can_reach_out |= {
+            Point3(x, y, z): True
+            for y, (x, z) in zip(
+                itertools.repeat(maxy + 1),
+                itertools.product(range(minx, maxx + 1), range(minz, maxz + 1)),
+            )
+        }
+        can_reach_out |= {
+            Point3(x, y, z): True
+            for z, (x, y) in zip(
+                itertools.repeat(minz - 1),
+                itertools.product(range(minx, maxx + 1), range(miny, maxy + 1)),
+            )
+        }
+        can_reach_out |= {
+            Point3(x, y, z): True
+            for z, (x, y) in zip(
+                itertools.repeat(maxz + 1),
+                itertools.product(range(minx, maxx + 1), range(miny, maxy + 1)),
+            )
+        }
+
+        for x, y, z in itertools.product(
+            range(minx, maxx + 1),
+            range(miny, maxy + 1),
+            range(minz, maxz + 1),
+        ):
+            p = Point3(x, y, z)
+            can_reach_out[p] = explore(p, can_reach_out)
+        return {p for p, can_reach in can_reach_out.items() if not can_reach}
+
+    cubes = {Point3.from_input(line) for line in input}
+    unreachable = compute_unreachable(cubes)
+
+    return sum(1 for p in cubes for n in Point3.neighbours(p) if n not in unreachable)
+
+
+def main() -> None:
+    input = sys.stdin.read().splitlines()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()