2023 Day 22 Part 1

2023/day22.py

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+import os
+
+from collections import defaultdict
+from dataclasses import dataclass
+from itertools import product
+from typing import Self, Iterator
+from pprint import pprint
+
+
+@dataclass
+class Point:
+    x: int
+    y: int
+    z: int
+
+    @classmethod
+    def parse(cls, text: str) -> Self:
+        x, y, z = [int(n) for n in text.split(',')]
+        return cls(x, y, z)
+
+    def __str__(self) -> str:
+        return f"({self.x}, {self.y}, {self.z})"
+
+    def __repr__(self) -> str:
+        return f"Point({self.x}, {self.y}, {self.z})"
+
+    def __hash__(self) -> int:
+        return hash((self.x, self.y, self.z))
+
+    def __lt__(self: Self, other: Self) -> bool:
+        return (self.z, self.x, self.y) < (other.z, other.x, other.y)
+
+
+@dataclass
+class Brick:
+    id: int
+    a: Point
+    b: Point
+
+    @classmethod
+    def parse(cls, id: int, text: str) -> Self:
+        a, b = text.split('~')
+        a = Point.parse(a)
+        b = Point.parse(b)
+        assert a.x <= b.x and a.y <= b.y and a.z <= b.z
+        return cls(id, a, b)
+
+    def __str__(self) -> str:
+        return f"{self.id} = {self.a} ~ {self.b}"
+
+    def __repr__(self) -> str:
+        return f"Brick({self.id}, {self.a}, {self.b})"
+
+    def points(self) -> Iterator[Point]:
+        for x in range(self.a.x, self.b.x+1):
+            for y in range(self.a.y, self.b.y+1):
+                for z in range(self.a.z, self.b.z+1):
+                    yield Point(x, y, z)
+
+
+@dataclass
+class Snapshot:
+    bricks: list[Brick]
+
+    @classmethod
+    def parse(cls, text: str) -> Self:
+        bricks = [
+            Brick.parse(i + 1, line)
+            for i, line in enumerate(text.splitlines())
+        ]
+        return cls(bricks)
+
+
+def part1(snap: Snapshot):
+    supports: dict[int, set[int]] = defaultdict(lambda: set())
+    tower: dict[Point, int] = {}
+    bricks: dict[int, Brick] = {}
+
+    lo = Point(0, 0, 0)
+    hi = Point(0, 0, 0)
+
+    for brick in snap.bricks:
+        bricks[brick.id] = brick
+        for p in brick.points():
+            tower[p] = brick.id
+
+            lo = Point(
+                min(lo.x, p.x),
+                min(lo.y, p.y),
+                min(lo.z, p.z),
+            )
+            hi = Point(
+                max(hi.x, p.x),
+                max(hi.y, p.y),
+                max(hi.z, p.z),
+            )
+
+    ids = list(bricks.keys())
+
+    changed = True
+    while changed:
+        changed = False
+        for id in ids:
+            brick = bricks[id]
+
+            new_z = None
+            for z in range(brick.a.z-1, 0, -1):
+                supported = False
+                surface = product(
+                    range(brick.a.x, brick.b.x + 1),
+                    range(brick.a.y, brick.b.y + 1),
+                )
+                for (x, y) in surface:
+                    if tower.get(Point(x, y, z)):
+                        supported = True
+                        break
+                if supported:
+                    new_z = z + 1
+                    break
+            else:
+                new_z = 1
+
+            dz = brick.a.z - new_z
+            assert dz >= 0
+
+            if dz == 0:
+                continue
+
+            for p in brick.points():
+                del tower[p]
+
+            brick.a.z -= dz
+            brick.b.z -= dz
+
+            for p in brick.points():
+                tower[p] = brick.id
+            changed = True
+
+    for brick in snap.bricks:
+        for z in range(brick.a.z-1, 0, -1):
+            surface = product(
+                range(brick.a.x, brick.b.x + 1),
+                range(brick.a.y, brick.b.y + 1),
+            )
+            for (x, y) in surface:
+                lower = tower.get(Point(x, y, z))
+                if not lower:
+                    continue
+                supports[brick.id].add(lower)
+            if supports[brick.id]:
+                break
+
+    solos: set[int] = set()
+    for v in supports.values():
+        if len(v) == 1:
+            solos.add(next(iter(v)))
+
+    return len(snap.bricks) - len(solos)
+
+
+def relpath(path: str) -> str:
+    return os.path.join(os.path.dirname(__file__), path)
+
+
+input_path = "./input/day22.txt"
+with open(relpath(input_path)) as f:
+    snap = Snapshot.parse(f.read())
+
+
+print(part1(snap))