HDU 1272 小希的迷宫

#include <bits/stdc++.h>
using namespace std;

const int maxn = 1e5 +10;
int f[maxn], A[maxn];
int N, M;
int cnt = 0;

void init() {
    for(int i = 1; i <= maxn; i ++)
        f[i] = i;
}

int Find(int x) {
    if(f[x] != x) f[x] = Find(f[x]);
    return f[x];
}

int Merge(int x, int y) {
    int fx = Find(x);
    int fy = Find(y);
    if(fx != fy) {
        f[fx] = fy;
        return 1;
    }
    else  return 0;
}

int main() {
    while(true) {
       init();
       int num = 0;
       bool flag = true;
       while(~scanf("%d%d", &N, &M)) {
            if(N == -1 && M == -1) return 0;
            else if(!N && !M) break;
            else if(flag) {
                if(!Merge(N, M)) flag = false;
                A[++ num] = N;
                A[++ num] = M;
            }
       }
        if(flag) {
                for(int j = 1; j <= num; j ++) {
                    if(Find(f[A[j]]) != Find(f[A[1]]))
                        flag = false;
                }
                if(flag) printf("Yes\n");
                else printf("No\n");
        }
        else printf("No\n");
    }
    return 0;
}