Jan 4, 2012

C Program to implement topological sort.

Write a c program to implement topological sort.
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. Read more about C Programming Language .
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#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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