并查集-朋友圈

package com.child.controller;

public class Test {

    public static int[] set;
    //3.component identifier for 0~N-1
    public static int find(int x){
        int i,j;
        int r = x;//所属队营，向上一层查找，
        while(set[r] != r){
            r = set[r];
        }
        i = r;
        while(set[i] != r){
            j = set[i];
            set[i] = r;
            r = j;
        }
        return r;

    }
    public static void union(int p,int q){
        int t = find(p);
        int h = find(q);
        if(t < h)
        {
            set[h] = t;
        }
        else
        {
            set[t] = h;
        }
    }
    public static int friends(int m,int[][] r){
        //1.初始化set集合　　　　 //初始化时，每个元素所属阵营为自己        set = new int[m+1];
        for(int i=1;i<=m;i++){
            set[i] = i;
        }
        //2.add connection between q and p
        for(int i=0;i<r.length;i++){
            union(r[i][0],r[i][1]);
        }

        int count = 0;
        for(int i = 1 ; i <= m ; ++i)
        {
            if(set[i] == i)
            {
                ++count;
            }
        }
        return count;

    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
            int n=5; int a[][]={{1,2},{2,3},{4,5},{2,4}};
            System.out.println(friends(5,a));
    }

}