Walls and Gates

def wallsAndGates(rooms):
    ROWS, COLS = len(rooms), len(rooms[0])
    visit = set()
    q = collections.deque()
    
    def addRoom(r, c):
        if (r < 0 or r == ROWS or c < 0 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
            addRoom(r + 1, c)
            addRoom(r - 1, c)
            addRoom(r, c + 1)
            addRoom(r, c - 1)
        dist += 1