Problem URL: Nearest exit from entrance in maze

We will start from the entrance, run BFS through the matrix and find the nearest exit. If we can't find the exit, we will return -1.

class Solution:
    def nearestExit(self, maze: List[List[str]], entrance: List[int]) -> int:
        ROWS, COLS = len(maze), len(maze[0])

        directions = [(0, 1), (1, 0), (0, -1), (-1, 0)]
        visited = set([tuple(entrance)])
        q = collections.deque([tuple(entrance)])

        steps = 0
        while q:
            qLen = len(q)
            for _ in range(qLen):
                r, c = q.pop()
                if (0 in [r, c] or r == ROWS-1 or c == COLS-1) and [r, c] != entrance:
                    return steps
                for dr, dc in directions:
                    x, y = r+dr, c+dc
                    if 0<=x<ROWS and 0<=y<COLS and maze[x][y] == '.' and (x, y) not in visited:
                        visited.add((x,y))
                        q.appendleft((x,y))
            steps += 1

        return -1

Time complexity: O(mn)
Space complexity: O(mn)