hdu 1269 迷宫城堡(强连通分量 Tarjan算法)

思路：Tarjan算法模板题。

#include<iostream>
#include<stdio.h>
#include<algorithm>
#include<string.h>
#include<vector>
#include<stack>
const int MAXN=10000+10;
using namespace std;
vector<int>mp[MAXN];
stack<int>S;
int n,m;
int _count;
int cnt;
bool mark[MAXN];
int dfn[MAXN];
int low[MAXN];

//求强连通分量tarjan
void Tarjan(int u){
    dfn[u]=low[u]=++cnt;
    mark[u]=true;
    S.push(u);
    for(int i=0;i<mp[u].size();i++){
        int v=mp[u][i];
        if(dfn[v]==0){
            Tarjan(v);
            low[u]=min(low[u],low[v]);
        }else if(mark[v]&&dfn[v]<low[u]){
            low[u]=dfn[v];
        }
    }
    if(low[u]==dfn[u]){
        _count++;
        int v;
        do{
            v=S.top();
            S.pop();
            mark[v]=false;
        }while(u!=v);
    }
}


int main(){
    while(~scanf("%d%d",&n,&m)){
        if(n==0&&m==0)break;
        for(int i=1;i<=n;i++)mp[i].clear();
        for(int i=1;i<=m;i++){
            int x,y;
            scanf("%d%d",&x,&y);
            mp[x].push_back(y);
        }
        memset(mark,false,sizeof(mark));
        memset(dfn,0,sizeof(dfn));
        memset(low,0,sizeof(low));
        _count=0;
        cnt=0;
        for(int i=1;i<=n;i++){
            if(dfn[i]==0){
                Tarjan(i);
            }
        }
        if(_count>1){
            printf("No\n");
        }else
            printf("Yes\n");
    }
    return 0;
}