Search Graph Nodes

思路：
比想象中的简单很多。因为只是找最近的而不是所有的target，在BFS过程中遇到的第一个target必然是最近的。然后给的graph 参数完全没用用到，影响了思路。
实现：
在判断当前node值是否是target时应该在内层循环外，不然初始node会被漏掉。

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