663. 墙和门

class Solution:
    """
    @param rooms: m x n 2D grid
    @return: nothing
    """
    def wallsAndGates(self, rooms):
        # write your code here
        #所有源点加进队列，如果是房间变成源点，也加入队列，循环队列，下一个房间rooms[x][y] = rooms[i][j] + 1
        
        #边界情况
        if not rooms: return
    
        #初始化
        m, n = len(rooms), len(rooms[0])
        queue = []
        
        #循环所有的点，把空房间加进来
        for i in range(m):
            for j in range(n):
                if (rooms[i][j] == 0):
                    queue.append([i, j])
            
        def bfs(x, y, value):
            if (x < 0 or y < 0 or x > m - 1 or  y > n - 1):
                return 
            
            #否则的话,如果是空房间的话 + 1,要在队列里面，接近源点，才会加 1，否则不变
            if (rooms[x][y] == 2147483647):
                queue.append([x, y])
                rooms[x][y] = value + 1 
        
        #pop队列，从前开始pop，如果是空房间则上一个源点 + 1的距离
        while queue:
            curr = queue.pop(0)
            x = curr[0]
            y = curr[1]
            value = rooms[x][y]
            
            #如果是INF，空房间，则上一个源点 + 1的距离
            bfs(x + 1, y, value)
            bfs(x - 1, y, value)
            bfs(x, y - 1, value)
            bfs(x, y + 1, value)
        
        return rooms