Introduction to Algorithms, Second Edition

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The University of Texas at Austin Breadth-first search Department of Computer Sciences Professor Vijaya Ramachandran Lecture 22 CS357: ALGORITHMS, Spring 2006 1 Breadth-first search and unweighted shortest paths We consider here the single-source shortest paths problem on an unweighted graph G = ( V, E ) (directed or undirected). Here, we are given as input a source vertex s V , and we need to find a path of shortest length from s to every other vertex in V . By definition, if there is no path from s to a vertex u , then the length of a shortest path from s to u is . The well-known algorithm to solve this problem is called breadth-first search . The length of a shortest path from s to u is called the distance from s to u , and is denoted by δ ( s, u ). We now study the breadth-first search algorithm that computes shortest-path dis- tances from source s . With a small modification, the algorithm also computes a shortest path tree rooted at s that gives the edges on a shortest path to each vertex; this is in the textbook,
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