Coding/E_Cyclic_Components.cpp at main · nishantlamba29/Coding · GitHub

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

int32_t main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

    int n, m;
    cin >> n >> m;
    vector<int> adj[n + 1];
    for(int i=0;i<m;i++) {
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }

    vector<bool> vis(n + 1);
    int ans = 0;
    bool flag;
    function<void(int, int)> dfs = [&](int node, int p) {
        vis[node] = 1;
        if(adj[node].size() != 2) flag = 0;
        for(auto & j : adj[node]) if(j != p) {
            if(!vis[j]) {
                dfs(j, node);
            }
        }
    };

    for(int i=1;i<=n;i++) {
        if(!vis[i]) {
            flag = 1;
            dfs(i, -1);
            if(flag) ans++;
        }
    }

    cout << ans << "\n";

    return 0;
}