Class DisjointSet

KruskalsAlgorithm.java:32–68

class DisjointSet {
    int parent[];
    int size[];
    DisjointSet(int nodes){
        this.parent = new int[nodes];
        this.size = new int[nodes];
        for(int i=0;i<nodes;i++){
            this.parent[i] = i;
            this.size[i] = 1;
        }
    }

    public int findRootParent(int node){
        if(node == parent[node]){
            return node;
        }
        parent[node] = findRootParent(parent[node]);
        return parent[node];
    }
    public boolean unionBySize(int node1, int node2){
        //1. find the root parent
        int rootParent1 = findRootParent(node1);
        int rootParent2 = findRootParent(node2);
        if(rootParent1==rootParent2){
            return false;
        }
        // 2, union of components
        if(size[rootParent1]<size[rootParent2]){
            parent[rootParent1] = rootParent2;
            size[rootParent2] += size[rootParent1];
        }else {
            parent[rootParent2] = rootParent1;
            size[rootParent1] += size[rootParent2];
        }
        return true;
    }
}