2024 day 16 part 1

README.md

@@ -15,7 +15,7 @@
 - 2021 - ★★★★★ ★★★★★ ★★★★★ ★★★
 - 2022 - ★★★★★ ★★★★★ ★★★★★ ★☆
 - 2023 - ★★★★★ ★★★★★ ★★★★★ ★★★☆
-- 2024 - ★★★★★ ★★★★★ ★★★★★
+- 2024 - ★★★★★ ★★★★★ ★★★★★ ☆
 
 ## How to use
 

src/year2024/day16a.py

@@ -0,0 +1,85 @@
+"""2024 - Day 16 Part 1: Reindeer Maze"""
+
+import sys
+from collections import deque
+from enum import StrEnum
+
+sys.setrecursionlimit(10_000)
+
+
+class Direction(StrEnum):
+    NORTH = "N"
+    EAST = "E"
+    SOUTH = "S"
+    WEST = "W"
+
+
+SHIFTS = {
+    # dr rc
+    Direction.NORTH: (-1, 0),
+    Direction.EAST: (0, +1),
+    Direction.SOUTH: (+1, 0),
+    Direction.WEST: (0, -1),
+}
+
+TO_LEFT = {
+    Direction.NORTH: Direction.WEST,
+    Direction.WEST: Direction.SOUTH,
+    Direction.SOUTH: Direction.EAST,
+    Direction.EAST: Direction.NORTH,
+}
+
+TO_RIGHT = {
+    Direction.NORTH: Direction.EAST,
+    Direction.EAST: Direction.SOUTH,
+    Direction.SOUTH: Direction.WEST,
+    Direction.WEST: Direction.NORTH,
+}
+
+
+def solve(task: str) -> int:
+    data = [list(line) for line in task.split("\n")]
+
+    rows = len(data)
+    cols = len(data[0])
+
+    start_r, start_c = rows - 2, 1
+    end_r, end_c = 1, cols - 2
+
+    to_process: deque[tuple[int, int, int, Direction]] = deque()
+    best_score: dict[tuple[int, int, Direction], int] = {}
+
+    to_process.append((start_r, start_c, 0, Direction.EAST))
+    best_score[(start_r, start_c, Direction.EAST)] = 0
+
+    result = sys.maxsize
+
+    while to_process:
+        r, c, score, direction = to_process.popleft()
+
+        if score >= result:
+            continue
+
+        if r == end_r and c == end_c:
+            result = min(result, score)
+            continue
+
+        if not (0 <= r < rows and 0 <= c < cols):
+            continue
+
+        if data[r][c] == "#":
+            continue
+
+        if (r, c, direction) in best_score:
+            old_score = best_score[(r, c, direction)]
+            if old_score < score:
+                continue
+
+        best_score[(r, c, direction)] = score
+
+        dr, dc = SHIFTS[direction]
+        to_process.append((r + dr, c + dc, score + 1, direction))
+        to_process.append((r, c, score + 1000, TO_LEFT[direction]))
+        to_process.append((r, c, score + 1000, TO_RIGHT[direction]))
+
+    return result

tests/src/year2024/test_day16a.py

@@ -0,0 +1,53 @@
+"""2024 - Day 16 Part 1: Reindeer Maze"""
+
+from textwrap import dedent
+
+from src.year2024.day16a import solve
+
+
+def test_solve_first():
+    task = dedent(
+        """
+        ###############
+        #.......#....E#
+        #.#.###.#.###.#
+        #.....#.#...#.#
+        #.###.#####.#.#
+        #.#.#.......#.#
+        #.#.#####.###.#
+        #...........#.#
+        ###.#.#####.#.#
+        #...#.....#.#.#
+        #.#.#.###.#.#.#
+        #.....#...#.#.#
+        #.###.#.#.#.#.#
+        #S..#.....#...#
+        ###############
+        """
+    ).strip()
+    assert solve(task) == 7036
+
+
+def test_solve_second():
+    task = dedent(
+        """
+        #################
+        #...#...#...#..E#
+        #.#.#.#.#.#.#.#.#
+        #.#.#.#...#...#.#
+        #.#.#.#.###.#.#.#
+        #...#.#.#.....#.#
+        #.#.#.#.#.#####.#
+        #.#...#.#.#.....#
+        #.#.#####.#.###.#
+        #.#.#.......#...#
+        #.#.###.#####.###
+        #.#.#...#.....#.#
+        #.#.#.#####.###.#
+        #.#.#.........#.#
+        #.#.#.#########.#
+        #S#.............#
+        #################
+        """
+    ).strip()
+    assert solve(task) == 11048