AoC 2024 day 16 part 1

aoc2024/src/day16/python/solution.py

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+# Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import math
+from typing import Sequence
+from collections import deque
+from dataclasses import dataclass
+
+type Position = tuple[int, int]  # (x,y)
+type Direction = tuple[int, int]  # (dx,dy) where -1 <= dx,dy <= 1.
+_START = 'S'
+_END = 'E'
+_WALL = '#'
+_SPACE = '.'
+_MOVE_POINTS = 1
+_TURN_POINTS = 1000
+_TURN_RIGHT_MAP = {
+  (0, -1): (1, 0),
+  (1, 0): (0, 1),
+  (0, 1): (-1, 0),
+  (-1, 0): (0, -1),
+}
+_TURN_LEFT_MAP = {v: k for k, v in _TURN_RIGHT_MAP.items()}
+
+
+def _charAt(maze: Sequence[str], pos: Position) -> str:
+  return maze[pos[1]][pos[0]]
+
+
+@dataclass
+class Node:
+  pos: Position
+  dir: Direction
+  score: int = 0
+
+
+def _bfs(maze: Sequence[str], start_pos: Position, start_dir: Direction, end_pos: Position) -> int:
+  min_score_at = {
+    start_pos: 0
+  }
+  queue = deque()
+  queue.append(Node(pos=start_pos, dir=start_dir))
+  while len(queue):
+    curr = queue.popleft()
+    current_score = curr.score + _MOVE_POINTS
+    if _charAt(maze, curr.pos) != _WALL:
+      left_dir = _TURN_LEFT_MAP.get(curr.dir)
+      right_dir = _TURN_RIGHT_MAP.get(curr.dir)
+      neighbours = (
+        Node(pos=(curr.pos[0] + curr.dir[0], curr.pos[1] + curr.dir[1]),
+             dir=curr.dir,
+             score=current_score),
+        Node(pos=(curr.pos[0] + left_dir[0], curr.pos[1] + left_dir[1]),
+             dir=left_dir,
+             score=current_score + _TURN_POINTS),
+        Node(pos=(curr.pos[0] + right_dir[0], curr.pos[1] + right_dir[1]),
+             dir=right_dir,
+             score=current_score + _TURN_POINTS),
+      )
+      for neighbour in neighbours:
+        if neighbour.pos not in min_score_at or current_score < min_score_at[neighbour.pos]:
+          min_score_at[neighbour.pos] = current_score
+          if neighbour.pos != end_pos:
+            queue.append(neighbour)
+  return min_score_at[end_pos]
+
+
+def _find_pos(maze: Sequence[str], value: str) -> Position:
+  """Finds the starting position represented by char 'S' in the maze."""
+  for y in range(len(maze)):
+    for x in range(len(maze[0])):
+      if _charAt(maze=maze, pos=(x, y)) == value:
+        return x, y
+  raise ValueError(f'value={value} not found in maze!')
+
+
+def get_min_score(maze: Sequence[str]) -> int:
+  start_pos = _find_pos(maze, _START)
+  end_pos = _find_pos(maze, _END)
+  start_dir = (1, 0)  # Right (East).
+  # DFS with recursion causes stack overflow.
+  return _bfs(maze=maze, start_pos=start_pos, start_dir=start_dir, end_pos=end_pos)

aoc2024/test/day16/python/example1.txt

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+###############
+#.......#....E#
+#.#.###.#.###.#
+#.....#.#...#.#
+#.###.#####.#.#
+#.#.#.......#.#
+#.#.#####.###.#
+#...........#.#
+###.#.#####.#.#
+#...#.....#.#.#
+#.#.#.###.#.#.#
+#.....#...#.#.#
+#.###.#.#.#.#.#
+#S..#.....#...#
+###############

aoc2024/test/day16/python/example2.txt

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+#################
+#...#...#...#..E#
+#.#.#.#.#.#.#.#.#
+#.#.#.#...#...#.#
+#.#.#.#.###.#.#.#
+#...#.#.#.....#.#
+#.#.#.#.#.#####.#
+#.#...#.#.#.....#
+#.#.#####.#.###.#
+#.#.#.......#...#
+#.#.###.#####.###
+#.#.#...#.....#.#
+#.#.#.#####.###.#
+#.#.#.........#.#
+#.#.#.#########.#
+#S#.............#
+#################

aoc2024/test/day16/python/test_solution.py

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+# Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import unittest
+
+from common.python3.AdventOfCodeTestCase import AdventOfCodeTestCase
+from aoc2024.src.day16.python.solution import get_min_score
+
+
+class TestSolution(AdventOfCodeTestCase):
+  def __init__(self, *args, **kwargs):
+    (super(TestSolution, self).__init__(__file__, *args,
+                                        **kwargs))
+
+  def test_part1_withExample_correct(self):
+    self.assertEqual(7036, get_min_score(self.examples[0]))
+
+  def test_part1_withSecondExample_correct(self):
+    self.assertEqual(11048, get_min_score(self.examples[1]))
+
+  def test_part1_withPuzzleInput_correct(self):
+    self.assertEqual(107512, get_min_score(self.input))
+
+
+if __name__ == '__main__':
+  unittest.main()