AoC 2025 day 6 part 1

aoc2024/src/day06/python/solution.py

@@ -0,0 +1,73 @@
+# 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.
+from typing import Sequence
+
+
+class World:
+  def __init__(self, world_map: Sequence[str]):
+    self._world_map = world_map
+    self._visited_pos = set()
+    # Assumption: guard always starts looking up (-y).
+    self._guard_pos: tuple[int, int] = self._find_guard_pos()
+    self._visited_pos.add(self._guard_pos)
+    self._guard_dir: tuple[int, int] = (-1, 0)  # Up.
+
+  def move(self) -> bool:
+    """Moves the guard and returns false when out of world map."""
+    next_pos = (self._guard_pos[0] + self._guard_dir[0], self._guard_pos[1] + self._guard_dir[1])
+    if not self._is_pos_valid(next_pos):
+      return False
+    if self._world_map[next_pos[0]][next_pos[1]] == '#':  # Obstacle.
+      self._turn_right()
+    else:
+      self._guard_pos = next_pos
+      self._visited_pos.add(self._guard_pos)
+    return True
+
+  def get_visited_pos(self) -> int:
+    """Returns the number of distinct positions the guard has been to."""
+    return len(self._visited_pos)
+
+  def _find_guard_pos(self) -> tuple[int, int]:
+    """Finds the starting guard position in the map."""
+    for y in range(len(self._world_map)):
+      for x in range(len(self._world_map[0])):
+        if self._world_map[y][x] == '^':
+          return y, x
+    raise ValueError('Guard not found!')
+
+  def _turn_right(self):
+    """Turns the guard's direction 90 degrees right."""
+    self._guard_dir = {
+      (-1, 0): (0, 1),  # Up -> Right
+      (0, 1): (1, 0),  # Right -> Down
+      (1, 0): (0, -1),  # Down -> Left
+      (0, -1): (-1, 0)  # Left -> Up
+    }.get(self._guard_dir)
+
+  def _is_pos_valid(self, pos: tuple[int, int]):
+    """Returns true if a position is within map bounds."""
+    return (0 <= pos[0] < len(self._world_map)
+            and 0 <= pos[1] < len(self._world_map[0]))
+
+
+def count_distinct_positions(world_map: Sequence[str]) -> int:
+  """Moves the guard until it exits the map.
+  A guard only moves forward. When facing an obstacle, it turns right.
+  Returns the positions the guard has been to."""
+  world = World(world_map)
+  while True:
+    if not world.move():
+      break
+  return world.get_visited_pos()

aoc2024/test/day06/python/example1.txt

@@ -0,0 +1,10 @@
+....#.....
+.........#
+..........
+..#.......
+.......#..
+..........
+.#..^.....
+........#.
+#.........
+......#...

aoc2024/test/day06/python/test_solution.py

@@ -0,0 +1,32 @@
+# 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 aoc2024.src.day06.python.solution import count_distinct_positions
+from common.python3.AdventOfCodeTestCase import AdventOfCodeTestCase
+
+
+class TestDay06Solution(AdventOfCodeTestCase):
+  def __init__(self, *args, **kwargs):
+    (super(TestDay06Solution, self).__init__(__file__, *args, **kwargs))
+
+  def test_part1_withExample_counts(self):
+    self.assertEqual(41, count_distinct_positions(self.examples[0]))
+
+  def test_part1_withPuzzleInput_counts(self):
+    self.assertEqual(5564, count_distinct_positions(self.input))
+
+
+if __name__ == '__main__':
+  unittest.main()