kruskal_algo.cpp

#include <bits/stdc++.h>
using namespace std;


class Edge {
public:
	int src, dest, weight;
};


class Graph {
public:
	

	int V, E;

	Edge* edge;
};


Graph* createGraph(int V, int E)
{
	Graph* graph = new Graph;
	graph->V = V;
	graph->E = E;

	graph->edge = new Edge[E];

	return graph;
}


class subset {
public:
	int parent;
	int rank;
};


int find(subset subsets[], int i)
{

	if (subsets[i].parent != i)
		subsets[i].parent
			= find(subsets, subsets[i].parent);

	return subsets[i].parent;
}


void Union(subset subsets[], int x, int y)
{
	int xroot = find(subsets, x);
	int yroot = find(subsets, y);


	if (subsets[xroot].rank < subsets[yroot].rank)
		subsets[xroot].parent = yroot;
	else if (subsets[xroot].rank > subsets[yroot].rank)
		subsets[yroot].parent = xroot;


	else {
		subsets[yroot].parent = xroot;
		subsets[xroot].rank++;
	}
}


int myComp(const void* a, const void* b)
{
	Edge* a1 = (Edge*)a;
	Edge* b1 = (Edge*)b;
	return a1->weight > b1->weight;
}


void KruskalMST(Graph* graph)
{
	int V = graph->V;
	Edge result[V]; // Tnis will store the resultant MST
	int e = 0; // An index variable, used for result[]
	int i = 0; // An index variable, used for sorted edges


	qsort(graph->edge, graph->E, sizeof(graph->edge[0]),
		myComp);


	subset* subsets = new subset[(V * sizeof(subset))];

	
	for (int v = 0; v < V; ++v)
	{
		subsets[v].parent = v;
		subsets[v].rank = 0;
	}


	while (e < V - 1 && i < graph->E)
	{

		Edge next_edge = graph->edge[i++];

		int x = find(subsets, next_edge.src);
		int y = find(subsets, next_edge.dest);

	
		if (x != y) {
			result[e++] = next_edge;
			Union(subsets, x, y);
		}
		
	}

	
	cout << "Following are the edges in the constructed "
			"MST\n";
	int minimumCost = 0;
	for (i = 0; i < e; ++i)
	{
		cout << result[i].src << " -- " << result[i].dest
			<< " == " << result[i].weight << endl;
		minimumCost = minimumCost + result[i].weight;
	}
	
	cout << "Minimum Cost Spanning Tree: " << minimumCost
		<< endl;
}

// Driver code
int main()
{

	int V = 4; // Number of vertices in graph
	int E = 5; // Number of edges in graph
	Graph* graph = createGraph(V, E);

	
	graph->edge[0].src = 0;
	graph->edge[0].dest = 1;
	graph->edge[0].weight = 10;


	graph->edge[1].src = 0;
	graph->edge[1].dest = 2;
	graph->edge[1].weight = 6;

	
	graph->edge[2].src = 0;
	graph->edge[2].dest = 3;
	graph->edge[2].weight = 5;

	// add edge 1-3
	graph->edge[3].src = 1;
	graph->edge[3].dest = 3;
	graph->edge[3].weight = 15;

	// add edge 2-3
	graph->edge[4].src = 2;
	graph->edge[4].dest = 3;
	graph->edge[4].weight = 4;


	
	KruskalMST(graph);

	return 0;
}