HDU-1232-畅通工程(并查集)

题目链接

/*
    Name:HDU-1232-畅通工程
    Copyright:
    Author:
    Date: 2018/4/12 15:38:11
    Description:
    并查集模板题 
*/
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
struct DisjoinSet {
    vector<int> father, rank;
    
    DisjoinSet(int n): father(n), rank(n) {
        for (int i=0; i<n; i++) {
            father[i] = i;
        }
    }
    
    int find(int v) {
        return father[v] = father[v] == v? v:find(father[v]);
    }
    
    void merge(int x, int y) {
        int a = find(x), b = find(y);
        if (rank[a] < rank[b]) {
            father[a] = b;
        } else {
            father[b] = a;
            if (rank[b] == rank[a]) {
                ++rank[a];
            }
        }
    }
} ; 
int main()
{
    int n, m;
    while (cin>>n>>m)  {
        DisjoinSet msf(1000+5);
        for (int i=0; i<m; i++) {
            int a,b;
            cin>>a>>b;
            msf.merge(a,b);
        }
        int ans = 0;
        for(int i=1; i<=n; i++){
            if(msf.father[i]==i) ans++;
        }
        cout<<ans-1<<endl;
    }
    return 0;
}