HDU 迷宫城堡 1269 （强连通图判定）

大意：问图中是不是所有两点都是任意可达的，i到j,同样j也要到达i.

就是缩成一个点即可，所以只需要判断scc是不是1即可。不需要找麻烦看度数。

#include<map>
#include<queue>
#include<cmath>
#include<cstdio>
#include<stack>
#include<iostream>
#include<cstring>
#include<algorithm>
#define LL int
#define inf 0x3f3f3f3f
#define eps 1e-8
#include<vector>
#define ls l,mid,rt<<1
#define rs mid+1,r,rt<<1|1

using namespace std;

const int Ma = 10100;
struct node{
int to,w,next;
}q[Ma*15];
int head[Ma*15],dfn[Ma],num[Ma],du[Ma],stk[Ma],vis[Ma],low[Ma];
int cnt,top,tim,scc,out[Ma];
bool bj;
void Add(int a,int b){
q[cnt].to = b;
q[cnt].next = head[a];
head[a] = cnt++;
}
void init(){
scc = cnt = top = 0;
tim = 1;bj = false;
memset(head,-1,sizeof(head));
memset(dfn,0,sizeof(dfn));
memset(num,0,sizeof(num));
memset(out,0,sizeof(out));
memset(vis,0,sizeof(vis));
memset(low,0,sizeof(low));
}
void Tarjan(int u){
low[u] = dfn[u] = tim++;
vis[u] = 1;
stk[top++] = u;
for(int i = head[u]; ~i ; i = q[i].next){
int v = q[i].to;
if(!vis[v]){
Tarjan(v);
low[u] = min(low[u],low[v]);
}
else
low[u] = min(low[u],dfn[v]);
}
if(low[u] == dfn[u]){
scc++;
while( top>0&&stk[top] != u ){
top--;
vis[stk[top] ] = 2;
num[stk[top] ] = scc;
}
}
}
int main(){
int n,m,i,j,k,a,b,cla;
while(~scanf("%d%d",&n,&m)){
if(!n&&!m) break;
init();
for(i = 0;i <m;++ i){
scanf("%d%d",&a,&b);
Add(a,b);
}
for(i = 1;i <= n;++i)
if(!dfn[i])
Tarjan(i);
if(scc==1)
puts("Yes");
else
puts("No");
}
return 0;
}