1 works

# Application of Kruskal's algorithm in Java

dashboard+ Project

Posted by @baristageek #java

```class Main
{
static int totalWeight = 0;
// A class to represent a graph edge
class Edge implements Comparable<Edge>
{
int src, dest, weight;

// Comparator function used for sorting edges based on
// their weight
public int compareTo(Edge compareEdge)
{
return this.weight-compareEdge.weight;
}
};

// A class to represent a subset for union-find
class subset
{
int parent, rank;
};

int V, E;	// V-> no. of vertices & E->no.of edges
Edge edge[]; // collection of all edges

// Creates a graph with V vertices and E edges
Main(int v, int e)
{
V = v;
E = e;
edge = new Edge[E];
for (int i=0; i<e; ++i)
edge[i] = new Edge();
}

// A utility function to find set of an element i
// (uses path compression technique)
int find(subset subsets[], int i)
{
// find root and make root as parent of i (path compression)
if (subsets[i].parent != i)
subsets[i].parent = find(subsets, subsets[i].parent);

return subsets[i].parent;
}

// A function that does union of two sets of x and y
// (uses union by rank)
void Union(subset subsets[], int x, int y)
{
int xroot = find(subsets, x);
int yroot = find(subsets, y);

// Attach smaller rank tree under root of high rank tree
// (Union by Rank)
if (subsets[xroot].rank < subsets[yroot].rank)
subsets[xroot].parent = yroot;
else if (subsets[xroot].rank > subsets[yroot].rank)
subsets[yroot].parent = xroot;

// If ranks are same, then make one as root and increment
// its rank by one
else
{
subsets[yroot].parent = xroot;
subsets[xroot].rank++;
}
}

// The main function to construct MST using Kruskal's algorithm
void KruskalMST()
{
Edge result[] = new Edge[V];  // Tnis will store the resultant MST
int e = 0;  // An index variable, used for result[]
int i = 0;  // An index variable, used for sorted edges
for (i=0; i<V; ++i)
result[i] = new Edge();

// Step 1:  Sort all the edges in non-decreasing order of their
// weight.  If we are not allowed to change the given graph, we
// can create a copy of array of edges
Arrays.sort(edge);

// Allocate memory for creating V ssubsets
subset subsets[] = new subset[V];
for(i=0; i<V; ++i)
subsets[i]=new subset();

// Create V subsets with single elements
for (int v = 0; v < V; ++v)
{
subsets[v].parent = v;
subsets[v].rank = 0;
}

i = 0;  // Index used to pick next edge

// Number of edges to be taken is equal to V-1
while (e < V - 1)
{
// Step 2: Pick the smallest edge. And increment the index
// for next iteration
Edge next_edge = new Edge();
next_edge = edge[i++];

int x = find(subsets, next_edge.src);
int y = find(subsets, next_edge.dest);

// If including this edge does't cause cycle, include it
// in result and increment the index of result for next edge
if (x != y)
{
result[e++] = next_edge;
Union(subsets, x, y);
}
}
int totalMSTWeight = 0;

for (i = 0; i < e; ++i) {
totalMSTWeight += result[i].weight;
}
//        System.out.println("total " + totalWeight);
//        System.out.println("MST " + totalMSTWeight);
System.out.println(totalWeight - totalMSTWeight);
}

// Driver Program
public static void main (String[] args) throws Exception
{

while (!in.equals("0 0")) {
totalWeight = 0;
String [] split = in.split(" ");
int V = Integer.parseInt(split);
int E = Integer.parseInt(split);

Main graph = new Main(V, E);

for (int i=0; i<E; i++) {
//System.out.println("split2: " + in);
String [] split2 = in.split(" ");
int a = Integer.parseInt(split2);
int b = Integer.parseInt(split2);
int c = Integer.parseInt(split2);

graph.edge[i].src = a;
graph.edge[i].dest = b;
graph.edge[i].weight = c;

totalWeight += c;
//System.out.println("source: "+a+", dest: " + b + " weight: "+ c);
}
graph.KruskalMST();