小希的迷宫 HDU 1272（并查集）

#include<stdio.h>
#include<string.h>
#include<iostream>
#include<algorithm>
#include<math.h>
#define maxn 110000
#define oo 0xfffffff
using namespace std;
int father[maxn],v[maxn];
int flag;

int Find(int x)
{
    while(x!=father[x])
        x=father[x];

    return x;
}

void solve(int a, int b)
{
    v[a] = v[b] = 1;
    if(a==b)
    {
        flag=1;
    }
    else
    {
        int ra = Find(a);
        int rb = Find(b);

        if(ra!=rb) father[rb]=ra;
        else flag = 1;
    }
}

int main()
{
    int a, b, fist;

    while(scanf("%d %d", &a, &b), a!=-1 || b!=-1)
    {
        if(a==0 && b==0)///空树也是树
        {
            printf("Yes\n");
            continue;
        }
        
        flag = 0;
        fist = a;
        memset(v, 0, sizeof(v));

        for(int i=1; i<maxn; i++)
            father[i] = i;

        solve(a, b);

        while(scanf("%d %d", &a, &b),a+b)
        {
            solve(a, b);
        }

        for(int i=1; i<maxn; i++)
        {
            if(Find(i)!=Find(fist) && v[i])
            {
                flag = 1;
                break;
            }
        }

        if(flag)  printf("No\n");

        else printf("Yes\n");
    }
    return 0;
}