hdu 1257 小希的迷宫 并查集

题目链接:

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

题意:

题解:

用并查集来判断是否都在一个集合里面，是否成环，就好了

代码:

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define MS(a) memset(a,0,sizeof(a))
#define MP make_pair
#define PB push_back
const int INF = 0x3f3f3f3f;
const ll INFLL = 0x3f3f3f3f3f3f3f3fLL;
inline ll read(){
    ll x=0,f=1;char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
    return x*f;
}
//////////////////////////////////////////////////////////////////////////
const int maxn = 1e5+10;

int mark[maxn],fa[maxn];

int find(int x){
    return fa[x]==x ? x : fa[x]=find(fa[x]);
}

bool Union(int u,int v){
    int t1 = find(u), t2 = find(v);
    if(t1 == t2) return false;
    fa[t1] = t2;
    return true;
}

int main(){
    int a,b;
    while(scanf("%d%d",&a,&b)){
        if(a==-1 && b==-1) break;
        if(a==0 && b==0){
            puts("Yes");
            continue;
        }

        MS(mark);
        for(int i=0; i<=maxn; i++)
            fa[i] = i;

        mark[a] = mark[b] = 1;
        fa[a] = b;
        int flag = 1;
        while(scanf("%d%d",&a,&b) && (a+b)){
            mark[a] = mark[b] = 1;
            if(Union(a,b)==0)
                flag = 0; 
        }
        if(flag==0)
            puts("No");
        else{
            int cnt = 0;
            for(int i=1; i<=maxn; i++){
                if(mark[i] && fa[i]==i)
                    cnt++;
            }
            if(cnt == 1)
                puts("Yes");
            else
                puts("No");
        }
    }

    return 0;
}