上海交大机试 第一题 Easy *并查集

#include<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<set>
using namespace std;

const int maxn = 1000000;
int father[maxn];
set<int>se;

int findfather(int a) {
	while (father[a] != a)
		a = father[a];
	return a;
}

void Union(int a, int b) {
	int aa = findfather(a);
	int bb = findfather(b);
	father[aa] = bb;
}

void init() {
	for (int i = 0; i < maxn; i++)
		father[i] = i;
}

int main() {
	int n,m;
	int cnt=0;
	init();
	while (cin >>m>>n) {
		Union(m, n);
		se.insert(m);
		se.insert(n);
	}
	for (set<int>::iterator it = se.begin(); it != se.end(); it++) {
		if (findfather(*it) == *it)
			cnt++;
	}
	cout << cnt << endl;
	return 0;
}