Codigos/977E.cpp at master · tfarnecim/Codigos · GitHub

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

typedef long long ll;
#define pb push_back

vector <ll> grafo[300000];
bool encontrou[300000];
vector <ll> passou;

void dfs(int v){

	passou.pb(v);
	encontrou[v] = true;

	for(int i=0;i<grafo[v].size();i++){

		ll adj = grafo[v][i];

		if(!encontrou[adj]){

			dfs(adj);

		}

	}

}

int main(){

	int n,m;

	cin >> n >> m;

	for(int i=0;i<m;i++){

		ll a,b;

		cin >> a >> b;

		grafo[a].pb(b);
		grafo[b].pb(a);

	}

	ll ans = 0;

	for(int i=1;i<=n;i++){

		if(!encontrou[i]){

			passou.clear();

			dfs(i);

			bool So2 = true;

			for(int i=0;i<passou.size();i++){

				if(grafo[ passou[i] ].size() != 2){
					So2 = false;
					break;
				}

			}

			if(So2){
				ans++;
			}

		}

	}

	cout << ans << endl;

	return 0;
}