hdoj 1272 小希的迷宫

并查集入门题

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

 
#include <iostream>
using namespace std;

#define MAX 100001

// father[x]表示x的父节点
int father[MAX];
// rank[x]表示x的秩
int rank[MAX];

// 初始化
void Make_Set(int n)
{
    for(int i=1; i<=n; ++i)
    {
        father[i] = i;
        rank[i] = 0;
    }
}

// 查找
int Find_Set(int x)
{
    if(x != father[x])
        return Find_Set(father[x]);
    return x;
}

// 合并
void Union(int x, int y)
{
    x = Find_Set(x);
    y = Find_Set(y);
    if(x == y)  // x,y在同一个集合
        return;
    if(rank[x] > rank[y])
        father[y] = x;
    else if(rank[x] < rank[y])
        father[x] = y;
    else
    {
        rank[y]++;
        father[x] = y;
    }
}

int main()
{
    //freopen("input.txt", "r", stdin);
    int a, b;
    while(scanf("%d %d", &a, &b))
    {
        if(a==-1 && b==-1)
            break;
        if(a==0 && b==0)
        {
            printf("Yes\n");
            continue;
        }
        Make_Set(MAX);
        rank[a]=1;
        rank[b]=1;
        Union(a, b);
        int flag=1;  // 表示是否有多条路
        while(scanf("%d %d", &a, &b) && (a+b))
        {
            rank[a]++;
            rank[b]++;
            if(Find_Set(a) == Find_Set(b))   // 判断两点是否有多条路
                flag = 0;
            Union(a, b);
        }
        int cnt = 0;
        for(int i=1; i<=MAX; ++i)
            if(rank[i] && Find_Set(i) == i)
                cnt++;
        if(flag && cnt==1)
            printf("Yes\n");
        else
            printf("No\n");

    }
    return 0;
}