hdu 1269 迷宫城堡 （图的联通，tarjan）

题目链接：hdu 1269

tarjan水题。我来复习一下tarjan。

#include<cstdio>#include<cstring>#include<iostream>#include<stack>using namespace std;#define maxn (10000+10)int N,M,tot,idx;int head[maxn],dfn[maxn],low[maxn],belong[maxn];bool vis[maxn];struct node{int v,next;}e[100000+10];int read(){int 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;}int k=0;void adde(int u,int v){e[k].v=v; e[k].next=head[u]; head[u]=k++;}stack<int>q;void tarjan(int x){dfn[x]=low[x]=++idx;vis[x]=1; q.push(x);for(int i=head[x];i!=-1;i=e[i].next){int v=e[i].v;if(!dfn[v]){tarjan(v); low[x]=min(low[x],low[v]);}else if(vis[v])low[x]=min(low[x],dfn[v]);}if(dfn[x]==low[x]){//注意要在遍历完x的子树的所有节点后再判断tot++; int now=0;while(now!=x){now=q.top(); q.pop();belong[now]=tot; vis[now]=0;}}}int main(){while(N=read()){M=read();memset(belong,0,sizeof(belong));memset(head,-1,sizeof(head));memset(vis,0,sizeof(vis));memset(dfn,0,sizeof(dfn));memset(low,0,sizeof(low));idx=0; tot=0; k=0;for(int i=1;i<=M;i++){int x=read(),y=read();adde(x,y);}for(int i=1;i<=N;i++)if(!dfn[i])tarjan(i);if(tot>1)printf("No\n");else printf("Yes\n");}return 0;}