HDU 1269 - 迷宫城堡

有向图的强连通图分量，Tarjan算法，模板题。

代码如下：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<vector>
#include<stack>
using namespace std;
const int Maxn = 10002;
const int MAX = 100002;
vector <int> G[MAX];
int pre[MAX], lowlink[MAX], sccno[MAX], dfs_clock, scc_cnt;
stack <int> S;
void dfs(int u)
{
    pre[u] = lowlink[u] = ++dfs_clock;
    S.push(u);
    for(int i=0; i<G[u].size(); i++)
    {
        int v = G[u][i];
        if(!pre[v])
        {
            dfs(v);
            lowlink[u] = min(lowlink[u], lowlink[v]);
        }
        else if(!sccno[v])
        {
            lowlink[u] = min(lowlink[u], pre[v]);
        }
    }
    if(lowlink[u] == pre[u])
    {
        scc_cnt++;
        for(;;)
        {
            int x = S.top();
            S.pop();
            sccno[x] = scc_cnt;
            if(x == u)
                break;
        }
    }
}
void find_scc(int n)
{
    dfs_clock = scc_cnt = 0;
    memset(sccno, 0, sizeof(sccno));
    memset(pre, 0, sizeof(pre));
    for(int i=1; i<=n; i++)
        if(!pre[i])
            dfs(i);
}

int main()
{
#ifdef test
    freopen("sample.txt", "r", stdin);
#endif
    int n, m;
    while(scanf("%d%d", &n, &m))
    {
        if(!n && !m)
            break;
        for(int i=1; i<=n; i++)
            G[i].clear();
        for(int i=1; i<=m; i++)
        {
            int u, v;
            scanf("%d%d", &u, &v);
            G[u].push_back(v);
        }
        find_scc(n);
        if(scc_cnt<=1)
            printf("Yes\n");
        else
            printf("No\n");
    }
    return 0;
}