HDU1269 迷宫城堡 （强连通图判定）

题意：判定给出的有向图是不是强连通图
Tarjan算法模板题目

#include<cstdio>#include<iostream>#include<algorithm>#include<cmath>#include<set>#include<map>#include<string>#include<cstring>#include<stack>#include<queue>#include<vector>#include<cstdlib>#define lson (rt<<1),L,M#define rson (rt<<1|1),M+1,R#define M ((L+R)>>1)#define cl(a,b) memset(a,b,sizeof(a));#define LL long long#define P pair<int,int>#define X first#define Y second#define pb push_back#define fread(zcc)  freopen(zcc,"r",stdin)#define fwrite(zcc) freopen(zcc,"w",stdout)using namespace std;const int maxn=100005;const int inf=999999;vector<int> G[maxn];int dfn[maxn],low[maxn],s[maxn];//依次对应，访问的序号，能到达的最早的，栈int belong[maxn];//连通分量的编号bool ins[maxn];//是否在栈里int cnt,num,top;//连通分量的编号，访问的序号，栈的指针void dfs(int u){    dfn[u]=low[u]=++num;    s[++top]=u;    ins[u]=true;    int N=G[u].size();    for(int i=0;i<N;i++){        int v=G[u][i];        if(!dfn[v]){            dfs(v);            low[u]=min(low[u],low[v]);        }        else if(ins[v]&&dfn[v]<low[u]){            low[u]=dfn[v];        }    }    if(low[u]==dfn[u]){        cnt++;        int v;        do{            v=s[top--];            ins[v]=false;            belong[v]=cnt;        }while(v!=u);    }}void Tarjan(int n){    cnt=num=top=0;    cl(dfn,0);    cl(ins,false);    cl(belong,0);    for(int i=1;i<=n;i++)if(!dfn[i]){        dfs(i);    }}int main(){    int n,m;    while(~scanf("%d%d",&n,&m)&&(n||m)){        for(int i=0;i<m;i++){            int a,b;            scanf("%d%d",&a,&b);            G[a].pb(b);        }        Tarjan(n);        for(int i=1;i<=n;i++){            if(belong[i]!=cnt){                puts("No");goto A;            }        }        puts("Yes");        A:;        for(int i=0;i<=n;i++)G[i].clear();    }    return 0;}