2018: d15: ex1: add solution

2018/d15/ex1/ex1.py

@@ -0,0 +1,192 @@
+#!/usr/bin/env python
+
+import dataclasses
+import enum
+import sys
+from typing import Iterator, NamedTuple
+
+
+class Point(NamedTuple):
+    x: int
+    y: int
+
+    # Returned in reading order
+    def neighbours(self) -> Iterator["Point"]:
+        for dx, dy in (
+            (-1, 0),
+            (0, -1),
+            (0, 1),
+            (1, 0),
+        ):
+            yield Point(self.x + dx, self.y + dy)
+
+
+class Unit(enum.StrEnum):
+    ELF = "E"
+    GOBLIN = "G"
+
+    def ennemy(self) -> "Unit":
+        if self == Unit.ELF:
+            return Unit.GOBLIN
+        if self == Unit.GOBLIN:
+            return Unit.ELF
+        assert False  # Sanity check
+
+
+@dataclasses.dataclass
+class UnitData:
+    hp: int = 200
+    power: int = 3
+
+
+def solve(input: str) -> int:
+    def parse(input: list[str]) -> tuple[set[Point], dict[Unit, set[Point]]]:
+        walls: set[Point] = set()
+        units: dict[Unit, set[Point]] = {u: set() for u in Unit}
+
+        for x, line in enumerate(input):
+            for y, c in enumerate(line):
+                p = Point(x, y)
+                if c in Unit:
+                    units[Unit(c)].add(p)
+                if c == "#":
+                    walls.add(p)
+
+        return walls, units
+
+    def double_bfs(
+        unit_type: Unit,
+        unit_pos: Point,
+        walls: set[Point],
+        units: dict[Unit, set[Point]],
+    ) -> Point | None:
+        def bfs(
+            start: Point,
+            targets: set[Point],
+            blockers: set[Point],
+        ) -> Point | None:
+            frontier = [start]
+            seen: set[Point] = set()
+            while frontier:
+                new_frontier: set[Point] = set()
+
+                for p in frontier:
+                    if p in targets:
+                        return p
+                    seen.add(p)
+                    for n in p.neighbours():
+                        if n in seen:
+                            continue
+                        if n in blockers:
+                            continue
+                        new_frontier.add(n)
+                frontier = sorted(new_frontier)
+
+            return None
+
+        blockers = walls | units[unit_type]
+        ennemies = units[unit_type.ennemy()]
+
+        # First BFS from start to square next to an ennemy
+        targets_in_range = {
+            n for ennemy in ennemies for n in ennemy.neighbours() if n not in blockers
+        }
+        if (target := bfs(unit_pos, targets_in_range, blockers)) is None:
+            return None
+
+        # Then back from chosen target to one of the movement squares
+        movement_squares = {n for n in unit_pos.neighbours() if n not in blockers}
+        return bfs(target, movement_squares, blockers)
+
+    def do_move(
+        unit_type: Unit,
+        unit_pos: Point,
+        walls: set[Point],
+        units: dict[Unit, set[Point]],
+        unit_data: dict[Point, UnitData],
+    ) -> Point:
+        # If already next to an ennemy, do not move
+        if any(n in units[unit_type.ennemy()] for n in unit_pos.neighbours()):
+            return unit_pos
+
+        new_pos = double_bfs(unit_type, unit_pos, walls, units)
+
+        # Nowhere to move to, no-op
+        if new_pos is None:
+            return unit_pos
+
+        assert new_pos != unit_pos  # Sanity check
+        assert unit_pos in units[unit_type]  # Sanity check
+        assert new_pos not in units[unit_type]  # Sanity check
+
+        # Make the movement in-place
+        units[unit_type] ^= {unit_pos, new_pos}
+        unit_data[new_pos] = unit_data.pop(unit_pos)
+
+        return new_pos
+
+    def do_attack(
+        unit_type: Unit,
+        unit_pos: Point,
+        units: dict[Unit, set[Point]],
+        unit_data: dict[Point, UnitData],
+    ) -> None:
+        # Look for an attack target
+        target = min(
+            (n for n in unit_pos.neighbours() if n in units[unit_type.ennemy()]),
+            key=lambda p: unit_data[p].hp,
+            default=None,
+        )
+
+        # If not in range, no-op
+        if target is None:
+            return
+
+        assert target not in units[unit_type]  # Sanity check
+        assert target in units[unit_type.ennemy()]  # Sanity check
+        assert unit_data[target].hp > 0  # Sanity check
+
+        # Make the attack in-place
+        unit_data[target].hp -= unit_data[unit_pos].power
+        # And if we killed it, remove it from `units`
+        if unit_data[target].hp <= 0:
+            units[unit_type.ennemy()].remove(target)
+            unit_data.pop(target)
+
+    def turn(
+        walls: set[Point],
+        units: dict[Unit, set[Point]],
+        unit_data: dict[Point, UnitData],
+    ) -> bool:
+        turn_order = sorted((p, u) for u, points in units.items() for p in points)
+        for p, u in turn_order:
+            # Don't do anything if the unit is dead
+            if p not in units[u]:
+                continue
+
+            # If no ennemies left, finish the turn early and indicate that we're done
+            if not units[u.ennemy()]:
+                return False
+
+            # Movements and attacks are made in-place
+            p = do_move(u, p, walls, units, unit_data)
+            do_attack(u, p, units, unit_data)
+
+        return True
+
+    walls, units = parse(input.splitlines())
+    unit_data = {p: UnitData() for points in units.values() for p in points}
+
+    turns = 0
+    while turn(walls, units, unit_data):
+        turns += 1
+    return turns * sum(data.hp for data in unit_data.values())
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()