CSES-1683 Planets and Kingdoms

Planets and Kingdoms

找出所有的点所属的强连通块编号

tarjan 模板

#include <iostream>
#include <vector>
#include <algorithm>
#include <stack>
using namespace std;
const int maxn = 1e5 + 10;
vector<int>gra[maxn];
int vis[maxn], scc[maxn], cnt_scc = 0;
int dfn[maxn], low[maxn], tp = 0;
stack<int>st;

void tarjan(int now)
{
    vis[now] = 1;
    st.push(now);
    dfn[now] = low[now] = ++tp;
    for(int nex : gra[now])
    {
        if(dfn[nex] == 0)
        {
            tarjan(nex);
            low[now] = min(low[now], low[nex]);
        }
        else if(vis[nex])
            low[now] = min(low[nex], low[now]);
    }
    if(low[now] == dfn[now])
    {
        cnt_scc++;
        while(st.top() != now)
        {
            int x = st.top();
            vis[x] = 0;
            st.pop();
            scc[x] = cnt_scc;
        }
        vis[now] = 0;
        st.pop();
        scc[now] = cnt_scc;
    }
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int n, m;
    cin >> n >> m;
    for(int i=0; i<m; i++)
    {
        int a, b;
        cin >> a >> b;
        gra[a].push_back(b);
    }
    for(int i=1; i<=n; i++)
        if(dfn[i] == 0) tarjan(i);
    cout << cnt_scc << endl;
    for(int i=1; i<=n; i++)
    {
        if(i != 1) cout << " ";
        cout << scc[i];
    }
    cout << endl;
    return 0;
}