Kruskal's Algorithm Implementation in C

This is the implementation of Kruskal’s Algorithm in C Programming Language. This algorithm is directly based on the generic MST (Minimum Spanning Tree) algorithm.

Kruskal’s algorithm is a greedy algorithm in graph theory that finds a minimum spanning tree for a connected weighted graph. It finds a subset of the edges that forms a tree that includes every vertex, where the total weight of all the edges in the tree is minimized.

Kruskal’s algorithm addresses two problems as mentioned below.

PROBLEM 1. Give a practical method for constructing a spanning subtree of minimum length.

PROBLEM 2. Give a practical method for constructing an unbranched spanning subtree of minimum length.

This algorithms is practically used in many fields such as Traveling Salesman Problem, Creating Mazes and Computer Networks etc.

Pseudo code for the Kruskal’s Algorithm

KRUSKAL(V, E, w)

A ← { }           ▷ Set A will ultimately contains the edges of the MST
for each vertex v in V
    do MAKE-SET(v)
sort E into non decreasing order by weight w
for each (u, v) taken from the sorted list
    do if FIND-SET(u) = FIND-SET(v)
        then A ← A ∪ {(u, v)}
            UNION(u, v)
return A

KRUSKAL(V, E, w)

A ← { } ▷ Set A will ultimately contains the edges of the MST

for each vertex v in V

do MAKE-SET(v)

sort E into non decreasing order by weight w

for each (u, v) taken from the sorted list

do if FIND-SET(u) = FIND-SET(v)

then A ← A ∪ {(u, v)}

UNION(u, v)

return A

C Programming Implementation of Kruskal’s Algorithm

    #include <stdio.h>
    #include <conio.h>
    #include <stdlib.h>
    int i,j,k,a,b,u,v,n,ne=1;
    int min,mincost=0,cost[9][9],parent[9];
    int find(int);
    int uni(int,int);
    void main()
    {
    	printf("\n\tImplementation of Kruskal's Algorithm\n");
    	printf("\nEnter the no. of vertices:");
    	scanf("%d",&n);
    	printf("\nEnter the cost adjacency matrix:\n");
    	for(i=1;i<=n;i++)
    	{
    		for(j=1;j<=n;j++)
    		{
    			scanf("%d",&cost[i][j]);
    			if(cost[i][j]==0)
    				cost[i][j]=999;
    		}
    	}
    	printf("The edges of Minimum Cost Spanning Tree are\n");
    	while(ne < n)
    	{
    		for(i=1,min=999;i<=n;i++)
    		{
    			for(j=1;j <= n;j++)
    			{
    				if(cost[i][j] < min)
    				{
    					min=cost[i][j];
    					a=u=i;
    					b=v=j;
    				}
    			}
    		}
    		u=find(u);
    		v=find(v);
    		if(uni(u,v))
    		{
    			printf("%d edge (%d,%d) =%d\n",ne++,a,b,min);
    			mincost +=min;
    		}
    		cost[a][b]=cost[b][a]=999;
    	}
    	printf("\n\tMinimum cost = %d\n",mincost);
    	getch();
    }
    int find(int i)
    {
    	while(parent[i])
    	i=parent[i];
    	return i;
    }
    int uni(int i,int j)
    {
    	if(i!=j)
    	{
    		parent[j]=i;
    		return 1;
    	}
    	return 0;
    }

#include <stdio.h>

#include <conio.h>

#include <stdlib.h>

int i,j,k,a,b,u,v,n,ne=1;

int min,mincost=0,cost[9][9],parent[9];

int find(int);

int uni(int,int);

void main()

{

printf("\n\tImplementation of Kruskal's Algorithm\n");

printf("\nEnter the no. of vertices:");

scanf("%d",&n);

printf("\nEnter the cost adjacency matrix:\n");

for(i=1;i<=n;i++)

{

for(j=1;j<=n;j++)

{

scanf("%d",&cost[i][j]);

if(cost[i][j]==0)

cost[i][j]=999;

}

printf("The edges of Minimum Cost Spanning Tree are\n");

while(ne < n)

{

for(i=1,min=999;i<=n;i++)

{

for(j=1;j <= n;j++)

{

if(cost[i][j] < min)

{

min=cost[i][j];

a=u=i;

b=v=j;

}

u=find(u);

v=find(v);

if(uni(u,v))

{

printf("%d edge (%d,%d) =%d\n",ne++,a,b,min);

mincost +=min;

}

cost[a][b]=cost[b][a]=999;

}

printf("\n\tMinimum cost = %d\n",mincost);

getch();

}

int find(int i)

{

while(parent[i])

i=parent[i];

return i;

}

int uni(int i,int j)

{

if(i!=j)

{

parent[j]=i;

return 1;

}

return 0;

}

Output of the C Program

   Implementation of Kruskal's Algorithm
 
Enter the no. of vertices:3  
 
Enter the cost adjacency matrix: 
9
8
7
6
5
4
3
2
3
The edges of Minimum Cost Spanning Tree are  
1 edge (3,2) =2  
2 edge (3,1) =3  
 
Minimum cost = 5