I’m taking a file of symbols:
pipes with openings on specific sides
the source: *
sinks: letters

and using BFS to find which sinks are connected to the source through the pipes, but it is only returning ‘ ‘.

My code starts by opening the file and parsing it into a grid. There is then a function to get the coordinates of neighboring cells. There’s a dictionary to denote which pipes can be connected to each other. Finally, there is a BFS function that starts at the source, *, and finds the sinks that are connected to it. However, the code is only returning ‘ ‘. What could be the issue?

def connected_sinks(file_path):
    from collections import defaultdict, deque

    def parse_file(file_path):
        grid = {}
        with open(file_path, 'r') as f:
            for line in f:
                obj, x, y = line.strip().split()
                x, y = int(x), int(y)
                grid[(x, y)] = obj
        return grid

    def get_neighbors(x, y):
        return [(x, y-1), (x, y+1), (x-1, y), (x+1, y)]

    def is_connected(cell, neighbor, direction):
        connections = {
            '═': {'left': '═╠╦╩╚╔', 'right': '═╣╦╩╝╗'},
            '║': {'up': '║╠╣╦╔╗', 'down': '║╠╣╩╚╝'},
            '╔': {'right': '═╣╦╩╝╗', 'down': '║╠╣╩╚╝'},
            '╗': {'left': '═╠╦╩╚╔', 'down': '║╠╣╩╚╝'},
            '╚': {'right': '═╣╦╩╝╗', 'up': '║╠╣╦╔╗'},
            '╝': {'left': '═╠╦╩╚╔', 'up': '║╠╣╦╔╗'},
            '╠': {'left': '═╠╦╩╚╔', 'right': '═╣╦╩╝╗', 'down': '║╠╣╩╚╝'},
            '╣': {'left': '═╠╦╩╚╔', 'right': '═╣╦╩╝╗', 'down': '║╠╣╩╚╝'},
            '╩': {'left': '═╠╦╩╚╔', 'right': '═╣╦╩╝╗', 'up': '║╠╣╦╔╗'},
            '╦': {'left': '═╠╦╩╚╔', 'right': '═╣╦╩╝╗', 'down': '║╠╣╩╚╝'}
        }
        if cell == '*' or neighbor == '*':
            return True
        if cell in connections and direction in connections[cell]:
            return neighbor in connections[cell][direction]
        return False

    def bfs(grid, start):
        queue = deque([start])
        visited = set([start])
        sinks = set()

        while queue:
            x, y = queue.popleft()
            for (nx, ny), direction in zip(get_neighbors(x, y), ['left', 'right', 'up', 'down']):
                if (nx, ny) in grid and (nx, ny) not in visited:
                    if is_connected(grid[(x, y)], grid[(nx, ny)], direction):
                        queue.append((nx, ny))
                        visited.add((nx, ny))
                        if grid[(nx, ny)].isalpha():
                            sinks.add(grid[(nx, ny)])
        return ''.join(sorted(sinks))

    grid = parse_file(file_path)
    source = next((pos for pos, val in grid.items() if val == '*'), None)
    if source:
        return bfs(grid, source)
    else:
        return ''