【HDU1269】tarjan算法求强联通分量

1.​​题目链接​​。判断图是不是一个强连通的图。tarjan算法对图的强连通分量计数即可。

#include<bits/stdc++.h>
#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
#pragma warning(disable:4996)
#define maxn 10001
vector<int >mp[maxn];
int vis[maxn];
int dfn[maxn];
int low[maxn];
int n, m, cnt, sig;
void init()
{
    memset(low, 0, sizeof(low));
    memset(dfn, 0, sizeof(dfn));
    memset(vis, 0, sizeof(vis));
    for (int i = 1; i <= n; i++)mp[i].clear();
}
void tarjan(int u)
{
    vis[u] = 1;
    low[u] = dfn[u] = cnt++;
    for (int i = 0; i < mp[u].size(); i++)
    {
        int v = mp[u][i];
        if (vis[v] == 0)tarjan(v);
        if (vis[v] == 1)low[u] = min(low[u], low[v]);
    }
    if (dfn[u] == low[u])
    {
        sig++;
    }
}
int main()
{
    while (~scanf("%d", &n))
    {
        if (n == 0)break;
        scanf("%d", &m);
        init();
        for (int i = 0; i < m; i++)
        {
            int x, y;
            scanf("%d%d", &x, &y);
            mp[x].push_back(y);
        }
        cnt = 1;
        sig = 0;
        for (int i = 1; i <= n; i++)
        {
            if (vis[i] == 0)
                tarjan(i);
        }
        if (sig == 1)
        {
            puts("Yes");
        }
        else
        {
            puts("No");
        }
    }
}