day 6

day_06/part_a.py

@@ -0,0 +1,58 @@
+import aocd
+from enum import Enum, nonmember
+
+class Direction(Enum):
+    NORTH = (0, -1)
+    WEST = (-1, 0)
+    SOUTH = (0, 1)
+    EAST = (1, 0)
+
+    @nonmember
+    def clockwise_from(d):
+        return list(Direction)[list(Direction).index(d) - 1]
+
+def facing(coords, direction):
+    return tuple(map(sum, zip(coords, direction.value)))
+
+def parse(data):
+    """
+    Given maze data, return
+    (Tuple of guard coords, set of obstacle coords, grid width, grid height)
+    """
+    guard = None
+    obstacles = set()
+
+    for y, row in enumerate(data.split('\n')):
+        for x, char in enumerate(row):
+            if char == '#':
+                obstacles.add((x, y))
+            elif char == '^':
+                guard = (x, y)
+    
+    return (guard, obstacles, x, y)
+
+def solve(data):
+    guard, obstacles, width, height = parse(data)
+    guard_direction = Direction.NORTH
+
+    visited = set()
+
+    while (0 <= guard[0] <= width) and (0 <= guard[1] <= height):
+        visited.add(guard)
+        while (facing_tile := facing(guard, guard_direction)) in obstacles:
+            guard_direction = Direction.clockwise_from(guard_direction)
+        guard = facing_tile
+
+    return sum(1 for _ in visited)
+
+
+if __name__ == '__main__':
+    puz = aocd.models.Puzzle(year=2024, day=6)
+
+    # data = puz.examples[0].input_data
+    data = puz.input_data
+
+    solution = solve(data)
+
+    print(solution)
+    aocd.submit(solution, year=2024, day=6, part='a')

day_06/part_b.py

@@ -0,0 +1,75 @@
+import aocd
+import collections
+from enum import Enum, nonmember
+
+class Direction(Enum):
+    NORTH = (0, -1)
+    WEST = (-1, 0)
+    SOUTH = (0, 1)
+    EAST = (1, 0)
+
+    @nonmember
+    def clockwise_from(d):
+        return list(Direction)[list(Direction).index(d) - 1]
+
+def facing(coords, direction):
+    return tuple(map(sum, zip(coords, direction.value)))
+
+def parse(data):
+    """
+    Given maze data, return
+    (Tuple of guard coords, set of obstacle coords, grid width, grid height)
+    """
+    guard = None
+    obstacles = set()
+
+    for y, row in enumerate(data.split('\n')):
+        for x, char in enumerate(row):
+            if char == '#':
+                obstacles.add((x, y))
+            elif char == '^':
+                guard = (x, y)
+    
+    return (guard, obstacles, x, y)
+
+def simulate(guard, obstacles, width, height, return_visited_tiles=False):
+    guard_direction = Direction.NORTH
+    visited = collections.defaultdict(set)
+
+    while (0 <= guard[0] <= width) and (0 <= guard[1] <= height):
+        visited[guard].add(guard_direction)
+        while (facing_tile := facing(guard, guard_direction)) in obstacles:
+            guard_direction = Direction.clockwise_from(guard_direction)
+
+        # Loop detection, can only be true in modified grids
+        if guard_direction in visited[facing_tile]:
+            return True
+
+        guard = facing_tile
+    
+    # No loop found
+
+    if return_visited_tiles:
+        return set(k for k,v in visited.items() if v)
+    
+    return False
+
+
+def solve(data):
+    guard, obstacles, width, height = parse(data)
+    
+    # Only bother checking positions that the guard crosses
+    potential_positions = simulate(guard, obstacles, width, height, return_visited_tiles=True)
+
+    return sum(simulate(guard, obstacles | {p}, width, height) for p in potential_positions)
+
+if __name__ == '__main__':
+    puz = aocd.models.Puzzle(year=2024, day=6)
+
+    # data = puz.examples[0].input_data
+    data = puz.input_data
+
+    solution = solve(data)
+
+    print(solution)
+    aocd.submit(solution, year=2024, day=6, part='b')