286-Walls-and-Gates.py

class Solution:
    """
    @param rooms: m x n 2D grid
    @return: nothing
    """
    def walls_and_gates(self, rooms: List[List[int]]):
        ROWS, COLS = len(rooms), len(rooms[0])
        visit = set()
        q = deque()

        def addRooms(r, c):
            if (min(r, c) < 0 or r == ROWS or c == COLS or
                (r, c) in visit or rooms[r][c] == -1):
                return
            visit.add((r, c))
            q.append([r, c])

        for r in range(ROWS):
            for c in range(COLS):
                if rooms[r][c] == 0:
                    q.append([r, c])
                    visit.add((r, c))

        dist = 0
        while q:
            for i in range(len(q)):
                r, c = q.popleft()
                rooms[r][c] = dist
                addRooms(r + 1, c)
                addRooms(r - 1, c)
                addRooms(r, c + 1)
                addRooms(r, c - 1)
            dist += 1