/* Program for creating a minimum spanning tree from Kruskal's algorithm */
#include<stdio.h>
#define MAX 20
struct edge
{
int u;
int v;
int weight;
struct edge *link;
}*front = NULL;
int father[MAX]; /*Holds father of each node */
struct edge tree[MAX]; /* Will contain the edges of spanning tree */
int n; /*Denotes total number of nodes in the graph */
int wt_tree=0; /*Weight of the spanning tree */
int count=0; /* Denotes number of edges included in the tree */
/* Functions */
void make_tree();
void insert_tree(int i,int j,int wt);
void insert_pque(int i,int j,int wt);
struct edge *del_pque();
main()
{
int i;
create_graph();
make_tree();
printf("Edges to be included in spanning tree are :\n");
for(i=1;i<=count;i++)
{
printf("%d->",tree[i].u);
printf("%d\n",tree[i].v);
}
printf("Weight of this minimum spanning tree is : %d\n", wt_tree);
}/*End of main()*/
create_graph()
{
int i,wt,max_edges,origin,destin;
printf("Enter number of nodes : ");
scanf("%d",&n);
max_edges=n*(n-1)/2;
for(i=1;i<=max_edges;i++)
{
printf("Enter edge %d(0 0 to quit): ",i);
scanf("%d %d",&origin,&destin);
if( (origin==0) && (destin==0) )
break;
printf("Enter weight for this edge : ");
scanf("%d",&wt);
if( origin > n || destin > n || origin<=0 || destin<=0)
{
printf("Invalid edge!\n");
i--;
}
else
insert_pque(origin,destin,wt);
}/*End of for*/
if(i<n-1)
{
printf("Spanning tree is not possible\n");
exit(1);
}
}/*End of create_graph()*/
void make_tree()
{
struct edge *tmp;
int node1,node2,root_n1,root_n2;
while( count < n-1) /*Loop till n-1 edges included in the tree*/
{
tmp=del_pque();
node1=tmp->u;
node2=tmp->v;
printf("n1=%d ",node1);
printf("n2=%d ",node2);
while( node1 > 0)
{
root_n1=node1;
node1=father[node1];
}
while( node2 >0 )
{
root_n2=node2;
node2=father[node2];
}
printf("rootn1=%d ",root_n1);
printf("rootn2=%d\n",root_n2);
if(root_n1!=root_n2)
{
insert_tree(tmp->u,tmp->v,tmp->weight);
wt_tree=wt_tree+tmp->weight;
father[root_n2]=root_n1;
}
}/*End of while*/
}/*End of make_tree()*/
/*Inserting an edge in the tree */
void insert_tree(int i,int j,int wt)
{
printf("This edge inserted in the spanning tree\n");
count++;
tree[count].u=i;
tree[count].v=j;
tree[count].weight=wt;
}/*End of insert_tree()*/
/*Inserting edges in the priority queue */
void insert_pque(int i,int j,int wt)
{
struct edge *tmp,*q;
tmp = (struct edge *)malloc(sizeof(struct edge));
tmp->u=i;
tmp->v=j;
tmp->weight = wt;
/*Queue is empty or edge to be added has weight less than first edge*/
if( front == NULL || tmp->weight < front->weight )
{
tmp->link = front;
front = tmp;
}
else
{
q = front;
while( q->link != NULL && q->link->weight <= tmp->weight )
q=q->link;
tmp->link = q->link;
q->link = tmp;
if(q->link == NULL) /*Edge to be added at the end*/
tmp->link = NULL;
}/*End of else*/
}/*End of insert_pque()*/
/*Deleting an edge from the priority queue*/
struct edge *del_pque()
{
struct edge *tmp;
tmp = front;
printf("Edge processed is %d->%d %d\n",tmp->u,tmp->v,tmp->weight);
front = front->link;
return tmp;
}/*End of del_pque()*/