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# notes40 - Jason D Ortiz Week 14 Notes CS251 Gustavo Depth...

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Jason D. Ortiz Week 14 Notes CS251 – Gustavo Depth First Search Assume the following graph: B E A D G C F DFS – visit the children before the siblings - Assign sequence num at the time of visit - Label the edges as back edge or discovery edge - Start at A A-1, B-2, (a->b = discovery), C-3, (b->c = discovery), (c->a = back),D-4,(c- >d = discovery),(d->b = back), E-5,(d->e = discovery),F-6,(e->f = discovery), (f->d = back),G-7,(f->g = discovery),(g->e = discovery) Algorithm (DFS) For each edge incident in the graph, do If edge is unexplored If vertex is unexplored Label edge as discovery Visit vertex Call DFS recursively Else Label as back edge **We can eliminate the recursion of DFS by using a stack Implementation(DFS) Void DFS(int n, int **am, int **seq, int ***disc, int ***back){ //input //n is the number of vertices //am is adjacency matrix as an array of pointers to rows //output //seq stores an array of seq numbers of the vertices visited //disc is a pointer to an array with the discovery edges //back is a pointer to an array with the back edges *seq = new int[n]; int *pseq = *seq;

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