Submission #65437367

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Source Code Expand

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

using ll=long long;
const ll oo=*(ll*)"?????????????????????????????????";
using dd=double;
const dd eps=1e-9;

using vl=vector<ll>;
using vvl=vector<vl>;
#define sz(x) ll((x).size())
#define all(x) begin(x),end(x)
#define pb push_back

#define mp make_pair
#define xx first
#define yy second

#define FOR(i,a,b) for(ll i=(a);i<(b);i++)
#define FORD(i,a,b) for(ll i=(b)-1;i>=(a);i--)

#define TR(X) ({ if(1) cerr << __LINE__ << ": " #X " = " << (X) << endl; })

void solve(){
	ll n,m; cin >> n >> m;
	vvl adj(n);
	
	FOR(j,0,m) {
		ll a,b; cin >> a >> b; a--; b--;
		adj[a].pb(b);
		adj[b].pb(a);
	}
	
	ll last=-1;
	ll cur=0;
	ll cnt=0;
	for(;;) {
		if(sz(adj[cur]) != 2) {
			cout << "No" << endl;
			return;
		}
		
		tie(cur,last) = mp(adj[cur][last==adj[cur][0]],cur);
		cnt++;
		if(cur == 0) {
			if(cnt == n) cout << "Yes" << endl;
			else cout << "No" << endl;
			return;
		}
		if(cnt == n) {
			cout << "No" << endl;
			return;
		}
		
	}
}

int main() { cin.sync_with_stdio(0); cin.tie(0);
	
	
	ll t=1; //cin >> t;
	while(t--) solve();
}

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