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cycle-in-graph.c
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cycle-in-graph.c
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/* A union-find algorithm to detect cycle in a graph
Concept is here: https://www.geeksforgeeks.org/union-find/
Below code is more optimized then above.
This code will is used in the kruskal's method to find Minimum Spanning Tree (MSM)
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// a structure to represent an edge in graph
struct Edge
{
int src, dest;
};
// a structure to represent a graph
struct Graph
{
// V-> Number of vertices, E-> Number of edges
int V, E;
// graph is represented as an array of edges
struct Edge* edge;
};
// Creates a graph with V vertices and E edges
struct Graph* createGraph(int V, int E)
{
struct Graph* graph =
(struct Graph*) malloc( sizeof(struct Graph) );
graph->V = V;
graph->E = E;
printf("V = %d , E = %d \n", graph->V, graph->E);
graph->edge =
(struct Edge*) malloc( graph->E * sizeof( struct Edge ) );
return graph;
}
// A utility function to find the subset of an element no
int find(int *parent, int no)
{
if(parent[no] == -1)
return no;
find(parent, parent[no]);
}
// A utility function to do union of two subsets
void Union(int x, int y, int **parent)
{
(*parent)[x] = y;
}
// The main function to check whether a given graph contains
// cycle or not
int isCycle(struct Graph *graph)
{
// Allocate memory for creating V subsets
int *parent = malloc(graph->V * sizeof(int));
// Initialize all subsets as single element sets
memset(parent, -1, sizeof(int) * graph->V);
// Iterate through all edges of graph, find subset of both
// vertices of every edge, if both subsets are same, then
// there is cycle in graph.
for(int i = 0; i < graph->E; i++)
{
int x = find(parent, graph->edge[i].src);
int y = find(parent, graph->edge[i].dest);
if(x == y)
return 1;
Union(x, y, &parent);
}
for(int i = 0; i < graph->V; i++)
{
printf("parent[%d] = %d \n", i, parent[i]);
}
return 0;
}
int main()
{
/* Let us create following graph
0
| \
| \
1-----2 */
int V = 3, E = 3;
struct Graph* graph = createGraph(V, E);
// add edge 0-1
graph->edge[0].src = 0;
graph->edge[0].dest = 1;
// add edge 1-2
graph->edge[1].src = 1;
graph->edge[1].dest = 2;
// add edge 0-2
graph->edge[2].src = 2;
graph->edge[2].dest = 0;
if (isCycle(graph))
printf( "graph contains cycle" );
else
printf( "graph doesn't contain cycle" );
return 0;
}