You are given am x n2D grid initialized with these three possible values.
-1- A wall or an obstacle. ? 0- A gate.
INF- Infinity means an empty room. We use the value231- 1 = 2147483647to representINFas you may assume that the distance to a gate is less than2147483647.
Fill each empty room with the distance to itsnearestgate. If it is impossible to reach a gate, it should be filled withINF.
For example, given the 2D grid:
INF? -1? 0? INF
INF INF INF? -1
INF? -1 INF? -1
0? -1 INF INF
After running your function, the 2D grid should be:
3? -1? 0? 1
2? 2? 1? -1
1? -1? 2? -1
0? -1? 3? 4
BFS， 把0 一起都放到隊列里， 然后開始循化隊列，如果 隊列里面的數字旁邊遇到INF， 則 把INF的值更改為隊列值+1， 再把這個被更新的INF放到隊列里面。
