hdu1269 tarjan算法

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#include <stdio.h>#include <string.h>#include <iostream>#include <algorithm>#include <vector>#include <queue>#include <set>#include <map>#include <string>#include <math.h>#include <stdlib.h>#include <time.h>using namespace std;const int N=1e4+10;const int M=1e5+10;struct Edge{int to,nxt;}edge[M];int head[N];int tot;void init(){memset(head,-1,sizeof head);tot=0;}void addEdge(int u,int v){edge[tot].to=v;edge[tot].nxt=head[u];head[u]=tot++;}int n,m;queue<int> Q;int vis[N];int id;int getId(int x){if(vis[x]==0) vis[x]=++id; return vis[x];}int low[N];void dfs(int u){low[u]=u;for(int k=head[u];~k;k=edge[k].nxt){int v=edge[k].to;if(!vis[v]){getId(v);dfs(v);} low[u]=min(low[u],low[v]);}}bool tarjan(){while(Q.size()) Q.pop();memset(vis,0,sizeof vis);id=0;getId(1);dfs(1);for(int i=1;i<=n;i++) if(vis[i]==0 || low[i]!=1) return false;return true;}int main(){    //freopen("in","r",stdin);    //freopen("out.txt","w",stdout);while(scanf("%d%d",&n,&m)==2){if(n==0) break;init();for(int i=1;i<=m;i++){int u,v;scanf("%d%d",&u,&v);addEdge(u,v);}puts(tarjan()?"Yes":"No");}        return 0;}

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