Let $ G=(V,E)$ be an undirected graph. given a pair of vertices $ s,t \in V$ , how can we construct a semi-streaming algorithm which determines is $ s$ and $ v$ are connected? Is there any way to construct such an algorithm which scans the input stream only once?

**Note** that a semi-streaming algorithm is presented an arbitrary order of the edges of $ G$ as a stream, and the algorithm can only access this input sequentially in the order it is given; it might process the input stream several times. The algorithm has a working memory consisting of $ O(nâ‹…polylogn)$ .