用CUDA实现BFS算法源码。CUDA是NV公司基于GPU的统一计算架构，BFS复杂度由CPU上的O(V+E)降为O(diameter)，直径diameter即图中root到leaf的最长距离。-This is the algorithm of BFS(breadth first search) on CUDA, and its time complexity is down to O(diameter) which diameter