PRIMSPT.CPP

/* Program for creating minimum spanning tree using Prim's algorithm.
This is and example of GREEDY METHOD */

#include<stdio.h>
#include<conio.h>
#include<stdlib.h>

#define MAX 10
#define TEMP 0
#define PERM 1
#define FALSE 0
#define TRUE 1
#define infinity 9999

struct node
{
int predecessor;
int dist; /*Distance from predecessor */
int status;
};

struct edge
{
int u;
int v;
};

int adj[MAX][MAX];
int n;

create_graph()
{
int i,max_edges,origin,destin,wt;

printf("Enter number of vertices : ");
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
{
adj[origin][destin]=wt;
adj[destin][origin]=wt;
}
}/*End of for*/
if(i<n-1)
{
printf("Spanning tree is not possible\n");
exit(1);
}
return 0;
}/*End of create_graph()*/

void display()
{
int i,j;
for(i=1;i<=n;i++)
{
for(j=1;j<=n;j++)
printf("%3d",adj[i][j]);
printf("\n");
}
}/*End of display()*/

/*This function returns TRUE if all nodes are permanent*/
int all_perm(struct node state[MAX] )
{
int i;
for(i=1;i<=n;i++)
if( state[i].status == TEMP )
return FALSE;
return TRUE;
}


int maketree(struct edge tree[MAX],int *weight)
{
struct node state[MAX];
int i,k,min,count,current,newdist;
int m;
int u1,v1;
*weight=0;
/*Make all nodes temporary*/
for(i=1;i<=n;i++)
{
state[i].predecessor=0;
state[i].dist = infinity;
state[i].status = TEMP;
}
/*Make first node permanent*/
state[1].predecessor=0;
state[1].dist = 0;
state[1].status = PERM;

/*Start from first node*/
current=1;
count=0; /*count represents number of nodes in tree */
while( all_perm(state) != TRUE ) /*Loop till all the nodes become PERM*/
{
for(i=1;i<=n;i++)
{
if ( adj[current][i] > 0 && state[i].status == TEMP )
{
if( adj[current][i] < state[i].dist )
{
state[i].predecessor = current;
state[i].dist = adj[current][i];
}
}
}/*End of for*/

/*Search for temporary node with minimum distance
and make it current node*/
min=infinity;
for(i=1;i<=n;i++)
{
if(state[i].status == TEMP && state[i].dist < min)
{
min = state[i].dist;
current=i;
}
}/*End of for*/

state[current].status=PERM;

/*Insert this edge(u1,v1) into the tree */
u1=state[current].predecessor;
v1=current;
count++;
tree[count].u=u1;
tree[count].v=v1;
/*Add wt on this edge to weight of tree */
*weight=*weight+adj[u1][v1];
}/*End of while*/
return (count);
}/*End of maketree()*/


void main()
{
int i,j;
int path[MAX];
int wt_tree,count;
struct edge tree[MAX];
clrscr();
create_graph();
printf("Adjacency matrix is :\n");
display();

count = maketree(tree,&wt_tree);

printf("Weight of spanning tree is : %d\n", wt_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);
}
getch();
}/*End of main()*/