HDU1269迷宫城堡

Tarjan算法解读：https://www.byvoid.com/zht/blog/scc-tarjan

#include<cstdio>
#include<cstring>
#include<iostream>
#include<cstring>
#include<vector>
#include<stack>
#include<algorithm>
using namespace std;
 
#define N 10003
int dfn[N],low[N],ins[N],Time,num;//ins是否在栈里
vector<int>gra[N];
stack<int>sta;
 
void Tarjan(int s)
{
    dfn[s] = low[s] = ++Time;
    sta.push(s);
    ins[s] = 1;
    for(int i=0;i<gra[s].size();i++)
    {
        int k = gra[s][i];
        if(dfn[k] == 0){
            Tarjan(k);
            low[s] = min(low[s] ,low[k]);
        }
        if(dfn[k] != 0 && ins[k] == 1){
            low[s] = min(low[s] ,dfn[k]);//low[s] = min(low[s] ,low[k]);好像也是对的
        }
    }
    if(dfn[s] == low[s])
    {
        num++;
        while(!sta.empty())
        {
            int temp = sta.top();
            sta.pop();
            ins[temp] = 0;
            if(temp == s) break;
        }
    }
}
 
int main()
{
    int n,m;
    while(scanf("%d%d",&n,&m)&&(n + m))
    {
        memset(dfn,0,sizeof(dfn));
        memset(ins,0,sizeof(ins));
        memset(low,0,sizeof(low));
        while(!sta.empty()) sta.pop();
        for(int i=1;i<=n;i++) gra[i].clear();
        int a,b;
        while(m--)
        {
            scanf("%d%d",&a,&b);
            gra[a].push_back(b);
        }
        num = Time = 0;
        for(int i=1;i<=n;i++)
        {
            if(dfn[i]==0) Tarjan(i);
        }
        if(num > 1) printf("No
");
        else printf("Yes
");
    }
}