C Program to implement topological sort


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Topological sort is the ordering vertices of a directed, acyclic graph(DAG), so that if there is an arc from vertex i to vertex j, then i appears before j in the linear ordering.

C Program

#include<stdio.h>
#define MAX 200
int n,adj[MAX][MAX];
int front = -1,rear = -1,queue[MAX];
void main() {
	int i,j = 0,k;
	int topsort[MAX],indeg[MAX];
	create_graph();
	printf(“The adjacency matrix is:\n”);
	display();
	for (i=1;i<+n;i++) {
		indeg[i]=indegree(i);
		if(indeg[i]==0)
		   insert_queue(i);
	}
	while(front<=rear) {
		k=delete_queue();
		topsort[j++]=k;
		for (i=1;i<=n;i++) {
			if(adj[k][i]==1) {
				adj[k][i]=0;
				indeg[i]=indeg[i]-1;
				if(indeg[i]==0)
				     insert_queue(i);
			}
		}
	}
	printf("Nodes after topological sorting are:\n");
	for (i=0;i<=n;i++)
	  printf("%d",topsort[i]);
	printf("\n");
}
create_graph() {
	int i,max_edges,origin,destin;
	printf("\n Enter number of vertices:");
	scamf("%d",&n);
	max_edges = n * (n - 1);
	for (i = 1;i <= max_edges;i++) {
		printf("\n Enter edge %d (00 to quit):",i);
		scanf("%d%d",&origin,&destin);
		if((origin == 0) && (destin == 0)) {
			printf("Invalid edge!!\n");
			i–;
		} else
		   adj[origin][destin] = 1;
	}
	return;
}
display() {
	int i,j;
	for (i = 0;i <= n;i++) {
		for (j = 1;jrear) {
			printf(“Queue Underflow”);
			return;
		} else {
			del_item = queue[front];
			front = front + 1;
			return del_item;
		}
	}
	int indegree(int node) {
		int i,in_deg = 0;
		for (i = 1;i <= n;i++)
		   if(adj[i][node] == 1)
		    in_deg++;
		returnin_deg;
	}





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