并查集 hdu 1856 示例

#include <iostream>
#include <string>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <vector>
#include <stack>
#include <deque>
#include <queue>
#include <bitset>
#include <list>
#include <map>
#include <set>
#include <iterator>
#include <algorithm>
#include <functional>
#include <utility>
#include <sstream>
#include <climits>
#include <cassert>
#define BUG puts("here!!!");

using namespace std;
const int N = 100005;
struct Node {
    int par;
    int sum;
};
int SUM;

Node p[2*N + 5];
void makeSet(int n) {
    for(int i = 0; i <= 2*n; i++) {
        p[i].par = i;
        p[i].sum = 1;
    }
    SUM = 1;
}
int find(int a) {
    if(a == p[a].par) return a;
    return p[a].par = find(p[a].par);
}
void union1(int a, int b) {
    int fa = find(a);
    int fb = find(b);
    if(fa != fb) {
        p[fa].par = fb;
        p[fb].sum += p[fa].sum;
    }
    if(p[fb].sum > SUM) {
        SUM = p[fb].sum;
    }
}
int main() {
    int n, a, b;
    while(scanf("%d", &n) == 1) {
        makeSet(n);
        while(n--) {
            scanf("%d%d", &a, &b);
            union1(a, b);
        }
        printf("%d\n", SUM);
    }
    return 0;
}

Sample Input
4
1 2
3 4
5 6
1 6
4
1 2
3 4
5 6
7 8
Sample Output
4
2