aoc2024day6.py

solution_day_6.py

with open(r'..\puzzle_inputs\day_6') as f:
    data = f.read()

grid_list = [[position for position in element] for element in data.split("\n")]

grid = {(x, y): grid_list[y][x] for y in range(len(grid_list)) for x in range(len(grid_list[0]))}

GRID_WIDTH, GRID_HEIGHT = (len(grid_list[0]), len(grid_list))

# directions
DIRECTIONS = {'^': (0, -1),
              '>': (1, 0),
              'v': (0, 1),
              '<': (-1, 0)}

NEXT_DIRECTIONS = {'^': '>',
                  '>': 'v',
                  'v': '<',
                  '<': '^'}

BLOCKAGE = '#'

# find START_POSITION
START_POSITION = None
START_DIRECTION = '^'

for y, row in enumerate(grid_list):
    if not START_POSITION:
        for x, position in enumerate(row):
            if position == '^':
                START_POSITION = (x, y)
                break

def trace_path(grid=grid, start_position=START_POSITION, start_direction=START_DIRECTION):
    steps_taken = set()
    current_position = start_position
    current_direction = start_direction
    # next_position = None
    while True:
            x_current, y_current = current_position
            x_direction, y_direction = DIRECTIONS[current_direction]
            next_position = (x_current + x_direction, y_current + y_direction)
            x_next, y_next = next_position
            if x_next < 0 or x_next > GRID_WIDTH - 1 or y_next < 0 or y_next > GRID_HEIGHT - 1:  # break out of loop if out of grid bounds
                break
            if grid[(x_next, y_next)] == BLOCKAGE:  # change direction if blockage hit
                current_direction = NEXT_DIRECTIONS[current_direction]
                continue
            current_position = next_position  # take a step
            steps_taken.add(next_position)
    return steps_taken

print(len(trace_path()))

# part 2

def loops_found(grid=grid, start_position=START_POSITION, start_direction=START_DIRECTION):
    num_of_possible_loops = 0
    for position in grid.keys():
        steps_taken = set()
        current_position = start_position
        current_direction = start_direction
        while True:
                x_current, y_current = current_position
                x_direction, y_direction = DIRECTIONS[current_direction]
                next_position = (x_current + x_direction, y_current + y_direction)
                x_next, y_next = next_position

                if x_next < 0 or x_next > GRID_WIDTH - 1 or y_next < 0 or y_next > GRID_HEIGHT - 1:  # break out of loop if out of grid bounds
                    break

                if grid[(x_next, y_next)] == BLOCKAGE or next_position == position:  # change direction if real or theoretical blockage is hit
                    current_direction = NEXT_DIRECTIONS[current_direction]
                    continue

                current_position = next_position  # take a step
                step_key = (next_position, current_direction)

                if step_key in steps_taken:  # loop found
                    num_of_possible_loops += 1
                    break

                steps_taken.add(step_key)
    return num_of_possible_loops

print(loops_found())