286. Walls and Gates

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Find all gates, and start from all gates together.

class Solution:
    def wallsAndGates(self, rooms: List[List[int]]) -> None:
        """
        Do not return anything, modify rooms in-place instead.
        """

        m = len(rooms)
        n = len(rooms[0])

        dq = deque()

        for i in range(m):
            for j in range(n):
                if rooms[i][j] == 0:
                    dq.append([(i, j), 0])

        
        while dq:
            lens = len(dq)

            for _ in range(lens):
                [(i, j), c] = dq.popleft()

                for x , y in [(0,1),(0,-1),(1,0),(-1,0)]:
                    if not (0 <= i+x<m and 0<=j+y<n):
                        continue
                    if rooms[i+x][j+y] != 2 ** 31 - 1:
                        continue
                    rooms[i+x][j+y] = c + 1
                    dq.append([(i+x, j+y), c+1])

            

        return