HDU ACM 1272 小希的迷宫(并查集)

http://acm.hdu.edu.cn/showproblem.php?pid=1272

题目要求有两个条件:1.在给定图中无环

　　　　　　　　　 2.给定的图有且仅有有1个连通分支

判断环:在输入时判断点a点b是否有相同的根节点,有相同根节点再加一条直接连通的边就有环.

判断连通分支数:判断有几个跟节点 if(father[i]==i)

#include <iostream>
using namespace std;
const int MAX = 100000 + 100;
int father[MAX];
int rank1[MAX];
int sign[MAX];
void Make_Set(int x)//初始化
{
    father[x] = x;
    rank1[x] = 0;
}

int Find_Set(int x)//找根节点
{
    int i=0;
    while(father[x] != x)
    {
        sign[i++] = x;
        x = father[x];
    }
    for(i;i>=1;i--)
    {
        father[sign[i-1]] = x;
    }
    return x;
}


void Union(int x,int y)//合并
{
    x = Find_Set(x);
    y = Find_Set(y);
    if(x == y)
    {
        return;
    }
    if(rank1[x] > rank1[y])
    {
        father[y] = x;
    }
    else if(rank1[x] < rank1[y])
    {
        father[x] = y;
    }
    else if(rank1[x] ==rank1[y]) 
    {
        father[x] = y;           
        rank1[y]++;             
    }
}

int main()
{
    while(1)
    {
        int i;
        int mark = 0;
        int used[MAX]={0};
        for(i=1;i<=MAX-1;i++)
        {
            Make_Set(i);
        }
        for(i=1;i<=MAX-1;i++)
        {
            int a,b;
            cin>>a>>b;
            if(a + b == 0)
            {
                break;
            }
            if(a == -1 && b == -1)
            {
                return 0;
            }
            used[a] = 1;
            used[b] = 1;
            int ra = Find_Set(a);
            int rb = Find_Set(b);
            if(ra == rb)
            {
                mark = 1;
            }
            Union(a,b);
        }
        int sum=0;
        for(i=1;i<=MAX-1;i++)
        {
            if(father[i]==i && used[i] == 1)
            {
                sum++;
            }
        }
        if(sum > 1 || mark == 1)
        {
            cout<<"No"<<endl;
        }
        else
        {
            cout<<"Yes"<<endl;
        }

    }
    return 0;
}