AoC 2024 day 15 part 1

aoc2024/src/day15/python/solution.py

@@ -0,0 +1,150 @@
+# 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
+
+type WarehouseMap = Sequence[Sequence[str]]
+type Position = tuple[int, int]  # (x,y)
+type Direction = tuple[int, int]  # (x,y)
+_ROBOT = '@'
+_BOX = 'O'
+_WALL = '#'
+_EMPTY = '.'
+
+
+def _opposite_dir(dir: Direction) -> Direction:
+  inverse = {
+    (0, 1): (0, -1),
+    (0, -1): (0, 1),
+    (-1, 0): (1, 0),
+    (1, 0): (-1, 0),
+  }
+  return inverse.get(dir)
+
+
+class Warehouse:
+  def __init__(self, warehouse_map: WarehouseMap, robot_moves: Sequence[Position]):
+    self._warehouse_map: list[list[str]] = [list(line) for line in warehouse_map]
+    self._width = len(self._warehouse_map[0])
+    self._height = len(self._warehouse_map)
+    self._robot_pos = self._find_robot_pos()
+    self._robot_moves = robot_moves
+    self._next_move_index = 0
+
+  def simulate(self) -> None:
+    """Simulates all robot moves in the warehouse."""
+    while self._next_move_index < len(self._robot_moves):
+      self._move_robot()
+      self._next_move_index += 1
+
+  def sum_all_boxes_gps_coordinates(self) -> int:
+    """Returns the sum of all the boxes' GPS coordinates.
+    A box GPS coordinate is 100 times its distance from the top edge of the
+    warehouse plus its distance from the left edge of the map.
+    """
+    result = 0
+    for y in range(self._height):
+      for x in range(self._width):
+        if self._charAt(pos=(x, y)) == _BOX:
+          result += 100 * y + x
+    return result
+
+  def _find_robot_pos(self) -> Position:
+    """Returns the position of the robot."""
+    for y in range(self._height):
+      for x in range(self._width):
+        if self._warehouse_map[y][x] == _ROBOT:
+          return x, y
+    raise ValueError('Robot not found!')
+
+  def _charAt(self, pos: Position) -> str:
+    """Returns what element is on the warehouse at a given position."""
+    return self._warehouse_map[pos[1]][pos[0]]
+
+  def _update(self, pos: Position, value: str) -> None:
+    """Updates a warehouse position with a given element."""
+    self._warehouse_map[pos[1]][pos[0]] = value
+
+  def _move_robot(self) -> None:
+    """Attempts to move robot one step. If the robot cannot move, it is a NOP."""
+    next_move = self._robot_moves[self._next_move_index]
+    next_pos = (self._robot_pos[0] + next_move[0], self._robot_pos[1] + next_move[1])
+    if self._charAt(next_pos) == _EMPTY:
+      self._update(self._robot_pos, _EMPTY)
+      self._robot_pos = next_pos
+      self._update(self._robot_pos, _ROBOT)
+    elif self._charAt(next_pos) == _BOX:
+      self._push(pos=next_pos, dir=next_move)
+      if self._charAt(next_pos) == _EMPTY:
+        self._update(self._robot_pos, _EMPTY)
+        self._robot_pos = next_pos
+        self._update(self._robot_pos, _ROBOT)
+
+  def _within_bounds(self, pos: Position):
+    """Returns true if a position is within warehouse bounds."""
+    return 0 <= pos[0] < self._width and 0 <= pos[1] < self._height
+
+  def _find_next_empty_pos(self, pos: Position, dir: Direction) -> Position | None:
+    """Returns the next empty space from a position towards a given direction."""
+    while self._within_bounds(pos):
+      if self._charAt(pos) == _WALL:
+        return None  # We hit a wall before an empty space.
+      if self._charAt(pos) == _EMPTY:
+        return pos
+      pos = (pos[0] + dir[0], pos[1] + dir[1])
+    # Empty space was not found.
+    return None
+
+  def _push(self, pos: Position, dir: Direction) -> None:
+    """Attempts to push boxes from given position towards given direction.
+    If there is no space to move boxes, it is a NOP."""
+    next_empty_pos = self._find_next_empty_pos(pos, dir)
+    if next_empty_pos is not None:
+      next_pos = next_empty_pos
+      while next_pos != pos:
+        self._update(next_pos, _BOX)
+        opposite_dir = _opposite_dir(dir)
+        next_pos = (next_pos[0] + opposite_dir[0], next_pos[1] + opposite_dir[1])
+      self._update(pos, _EMPTY)
+
+
+def _parse(input: Sequence[str]) -> tuple[WarehouseMap, Sequence[Position]]:
+  """Parses the input and returns the warehouse map and sequence of robot moves."""
+  is_map = True
+  warehouse_map = []
+  robot_moves = []
+  for line in input:
+    if line == '':
+      is_map = False
+    if is_map:
+      warehouse_map.append(line)
+    else:
+      for i in line:
+        if i == '^':  # Up.
+          robot_moves.append((0, -1))
+        if i == '<':  # Left.
+          robot_moves.append((-1, 0))
+        if i == '>':  # Right.
+          robot_moves.append((1, 0))
+        if i == 'v':  # Down.
+          robot_moves.append((0, 1))
+  return tuple(warehouse_map), tuple(robot_moves)
+
+
+def sum_all_boxes_gps_coordinates(input: Sequence[str]) -> int:
+  """Simulates all the robot moves in the warehouse and returns the sum of
+  all boxes GPS coordinates at the end state."""
+  warehouse_map, robot_moves = _parse(input)
+  warehouse = Warehouse(warehouse_map, robot_moves)
+  warehouse.simulate()
+  return warehouse.sum_all_boxes_gps_coordinates()

aoc2024/test/day15/python/example1.txt

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+########
+#..O.O.#
+##@.O..#
+#...O..#
+#.#.O..#
+#...O..#
+#......#
+########
+
+<^^>>>vv<v>>v<<

aoc2024/test/day15/python/example2.txt

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+##########
+#..O..O.O#
+#......O.#
+#.OO..O.O#
+#[email protected].#
+#O#..O...#
+#O..O..O.#
+#.OO.O.OO#
+#....O...#
+##########
+
+<vv>^<v^>v>^vv^v>v<>v^v<v<^vv<<<^><<><>>v<vvv<>^v^>^<<<><<v<<<v^vv^v>^
+vvv<<^>^v^^><<>>><>^<<><^vv^^<>vvv<>><^^v>^>vv<>v<<<<v<^v>^<^^>>>^<v<v
+><>vv>v^v^<>><>>>><^^>vv>v<^^^>>v^v^<^^>v^^>v^<^v>v<>>v^v^<v>v^^<^^vv<
+<<v<^>>^^^^>>>v^<>vvv^><v<<<>^^^vv^<vvv>^>v<^^^^v<>^>vvvv><>>v^<<^^^^^
+^><^><>>><>^^<<^^v>>><^<v>^<vv>>v>>>^v><>^v><<<<v>>v<v<v>vvv>^<><<>^><
+^>><>^v<><^vvv<^^<><v<<<<<><^v<<<><<<^^<v<^^^><^>>^<v^><<<^>>^v<v^v<v^
+>^>>^v>vv>^<<^v<>><<><<v<<v><>v<^vv<<<>^^v^>^^>>><<^v>>v^v><^^>>^<>vv^
+<><^^>^^^<><vvvvv^v<v<<>^v<v>v<<^><<><<><<<^^<<<^<<>><<><^^^>^^<>^>v<>
+^^>vv<^v^v<vv>^<><v<^v>^^^>>>^^vvv^>vvv<>>>^<^>>>>>^<<^v>^vvv<>^<><<v>
+v^^>>><<^^<>>^v^<v^vv<>v^<<>^<^v^v><^<<<><<^<v><v<>vv>>v><v^<vv<>v^<<^