HDU1269tarjan求强连通分量

Posted 2021-08-20 hesorchen

题目

HDU 1269

给一张有向图问是否每个点对都能互相到达。

tarjan求强连通分量模板。

代码

#include <bits/stdc++.h>
using namespace std;

const int N = 10000 + 5;
vector<int> edge[N];
int dfn[N], low[N], ct, cnt;
bool instack[N];
stack<int> st;
void tarjan(int u)
{
    dfn[u] = low[u] = ++ct;
    st.push(u);
    instack[u] = 1;
    for (auto v : edge[u])
    {
        if (!dfn[v])
        {
            tarjan(v);
            low[u] = min(low[u], low[v]);
        }
        else if (instack[v])
        {
            low[u] = min(low[u], dfn[v]);
        }
    }
    if (low[u] == dfn[u])
    {
        ++cnt;
        int node;
        do
        {
            node = st.top();
            st.pop();
            instack[node] = 0;
        } while (dfn[node] != low[node]);
    }
}
int main()
{
    int n, m;
    while (cin >> n >> m, n + m)
    {
        memset(dfn, 0, sizeof dfn);
        memset(low, 0, sizeof low);
        memset(instack, 0, sizeof instack);
        for (int i = 1; i <= n; i++)
            edge[i].clear();
        ct = cnt = 0;
        for (int i = 1; i <= m; i++)
        {
            int u, v;
            cin >> u >> v;
            edge[u].emplace_back(v);
        }
        for (int i = 1; i <= n; i++)
            if (!dfn[i])
                tarjan(i);
        puts(cnt == 1 ? "Yes" : "No");
    }
    return 0;
}