HDU1269 迷宫城堡（tarjan判断强连通）

裸的判断强连通，如果整个图中只有一个强连通分量，就“Yes”，否则“No”

tarjan的代码：

#include<cstdio>
#include<cstring>
#include<stack>
using namespace std;

const int N = 10001;

struct Edge{
int s,e,next;
}edge[10*N];

int n,m,e_num,vis_num,cnt,head
,instack
,low
,tim
;

void AddEdge(int a,int b){
edge[e_num].s=a; edge[e_num].e=b; edge[e_num].next=head[a]; head[a]=e_num++;
}

void getmap(){
int a,b;
memset(instack,0,sizeof(instack));
memset(low,0,sizeof(low));
memset(tim,-1,sizeof(tim));

e_num=0;
memset(head,-1,sizeof(head));
while(m--){
scanf("%d%d",&a,&b);
AddEdge(a,b);
}
}

stack <int> st;
void tarjan(int x){
int j;
tim[x]=low[x]=++vis_num;
instack[x]=1;
st.push(x);
for(j=head[x];j!=-1;j=edge[j].next){
int u=edge[j].e;
if(tim[u]==-1){
tarjan(u);
if(low[x]>low[u])low[x]=low[u];
}
else if(instack[u] && low[x]>tim[u])low[x]=tim[u];
}
if(low[x]==tim[x]){
cnt++;
do{
j=st.top();
st.pop();
instack[j]=0;
}while(j!=x);
}
}

void solve(){
int i;
vis_num=cnt=0;
for(i=1;i<=n;i++){
if(tim[i]==-1)tarjan(i);
}
if(cnt==1)printf("Yes\n");
else printf("No\n");
}
int main()
{
while(scanf("%d%d",&n,&m),n+m)
{
getmap();
solve();
}
return 0;
}