Day 18: RAM Run

README.md

@@ -22,4 +22,4 @@ Development occurs in language-specific directories:
 |[Day15.hs](hs/src/Day15.hs)|[Day15.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day15.kt)|[day15.py](py/aoc2024/day15.py)|[day15.rs](rs/src/day15.rs)|
 |[Day16.hs](hs/src/Day16.hs)|[Day16.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day16.kt)|[day16.py](py/aoc2024/day16.py)|[day16.rs](rs/src/day16.rs)|
 |[Day17.hs](hs/src/Day17.hs)|[Day17.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day17.kt)|[day17.py](py/aoc2024/day17.py)|[day17.rs](rs/src/day17.rs)|
-|[Day18.hs](hs/src/Day18.hs)|[Day18.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day18.kt)|||
+|[Day18.hs](hs/src/Day18.hs)|[Day18.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day18.kt)|[day18.py](py/aoc2024/day18.py)||

py/aoc2024/day18.py

@@ -0,0 +1,86 @@
+"""
+Day 18: RAM Run
+"""
+
+from collections import deque
+from typing import Iterable
+
+SAMPLE_INPUT = """
+5,4
+4,2
+4,5
+3,0
+2,1
+6,3
+2,4
+1,5
+0,6
+3,3
+2,6
+5,1
+1,2
+5,5
+2,5
+6,5
+1,4
+0,4
+6,4
+1,1
+6,1
+1,0
+0,5
+1,6
+2,0
+"""
+
+
+def _parse(data: str) -> list[tuple[int, int]]:
+    return [
+        (int(line[: (i := line.index(","))]), int(line[i + 1 :]))
+        for line in data.splitlines()
+        if "," in line
+    ]
+
+
+def findpath(obstacles: Iterable[tuple[int, int]], size: int) -> list[tuple[int, int]]:
+    visited, queue = set(obstacles), deque(([(0, 0)],))
+    while queue:
+        path = queue.popleft()
+        x, y = pos = path[-1]
+        if x == size and y == size:
+            return path
+        if pos in visited:
+            continue
+        visited.add(pos)
+        for pos in ((x - 1, y), (x, y - 1), (x, y + 1), (x + 1, y)):
+            x, y = pos
+            if 0 <= x <= size and 0 <= y <= size:
+                queue.append(path + [(x, y)])
+    return None
+
+
+def part1(data: str, size: int = 70, n: int = 1024) -> int:
+    """
+    >>> part1(SAMPLE_INPUT, 6, 12)
+    22
+    """
+    return len(findpath(_parse(data)[:n], size)) - 1
+
+
+def part2(data: str, size: int = 70) -> str:
+    """
+    >>> part2(SAMPLE_INPUT, 6)
+    '6,1'
+    """
+    obstacles, i = _parse(data), 0
+    while True:
+        path = findpath(obstacles[: i + 1], size)
+        if path is None:
+            x, y = obstacles[i]
+            return f"{x},{y}"
+        path = set(path)
+        while obstacles[i] not in path:
+            i += 1
+
+
+parts = (part1, part2)

py/pyproject.toml

@@ -41,6 +41,7 @@ day14 = "aoc2024.day14:parts"
 day15 = "aoc2024.day15:parts"
 day16 = "aoc2024.day16:parts"
 day17 = "aoc2024.day17:parts"
+day18 = "aoc2024.day18:parts"
 
 [build-system]
 requires = ["poetry-core"]