hdu 1269 迷宫城堡 强连通分量

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

const int maxn = 10000 + 10;

vector<int> G[maxn], G2[maxn];
vector<int> S;
int vis[maxn], sccno[maxn], scc_cnt;

void dfs1(int u)
{
if(vis[u]) return;
vis[u] = 1;
for(int i = 0; i < G[u].size(); i++) dfs1(G[u][i]);
S.push_back(u);
}

void dfs2(int u)
{
if(sccno[u]) return;
sccno[u] = scc_cnt;
for(int i = 0; i < G2[u].size(); i++) dfs2(G2[u][i]);
}

void find_scc(int n)
{
scc_cnt = 0;
S.clear();
memset(sccno, 0, sizeof(sccno));
memset(vis, 0, sizeof(vis));
for(int i = 0; i < n; i++) dfs1(i);
for(int i = n-1; i >= 0; i--)
if(!sccno[S[i]]) { scc_cnt++; dfs2(S[i]); }
}

int main()
{
int T, n, m;
while(1)
{
scanf("%d%d", &n, &m);
if(n==0&&m==0) break;
for(int i = 0; i < n; i++) { G[i].clear(); G2[i].clear(); }
for(int i = 0; i < m; i++)
{
int u, v;
scanf("%d%d", &u, &v); u--; v--;
G[u].push_back(v); G2[v].push_back(u);
}

find_scc(n);

if(scc_cnt == 1) printf("Yes\n");
else printf("No\n");
}
return 0;
}