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POerror in the code given in skiena's book for the application of dfs to find a cycle in a graph
 

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  1. POerror in the code given in skiena's book for the application of dfs to find a cycle in a graph
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    <p>This is the code for dfs.</p> <pre><code>bool processed[MAXV+1]; /* which vertices have been processed */ bool discovered[MAXV+1]; /* which vertices have been found */ int parent[MAXV+1]; /* discovery relation */ #define MAXV 1000 /* maximum number of vertices */ typedef struct { int y; /* adjacency info */ int weight; /* edge weight, if any */ struct edgenode *next; /* next edge in list */ } edgenode; typedef struct { edgenode *edges[MAXV+1]; /* adjacency info */ int degree[MAXV+1]; /* outdegree of each vertex */ int nvertices; /* number of vertices in graph */ int nedges; /* number of edges in graph */ bool directed; /* is the graph directed? */ } graph; dfs(graph *g, int v) { edgenode *p; /* temporary pointer */ int y; /* successor vertex */ if (finished) return; /* allow for search termination */ discovered[v] = TRUE; time = time + 1; entry_time[v] = time; process_vertex_early(v); p = g-&gt;edges[v]; while (p != NULL) { y = p-&gt;y; if (discovered[y] == FALSE) { parent[y] = v; process_edge(v,y); dfs(g,y); } else if ((!processed[y]) || (g-&gt;directed)) process_edge(v,y); if (finished) return; p = p-&gt;next; } process_vertex_late(v); time = time + 1; exit_time[v] = time; processed[v] = TRUE; } </code></pre> <p>And for finding the cycles it has modified the process edge function like below</p> <pre><code>process_edge(int x, int y) { if (parent[x] != y) { /* found back edge! */ printf("Cycle from %d to %d:",y,x); find_path(y,x,parent); printf("\n\n"); finished = TRUE; } } </code></pre> <p>Now imagine a small tree with just 2 leaf nodes and one root. When this tree is subjected to this function, I believe it will say that it has cycles. which is wrong !! Please correct me if i am wrong. Thanks.</p>
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