제출 #844801

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
844801		irmuun	Duathlon (APIO18_duathlon)	C++17	0 / 100	42 ms	7260 KiB

count_triplets

#include<bits/stdc++.h>
 
using namespace std;
 
#define ll long long
#define pb push_back
#define ff first
#define ss second
#define all(s) s.begin(),s.end()
#define rall(s) s.rbegin(),s.rend()

int main(){
    ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
    ll n,m;
    cin>>n>>m;
    vector<ll>adj[n+1];
    for(ll i=1;i<=m;i++){
        ll u,v;
        cin>>u>>v;
        adj[u].pb(v);
        adj[v].pb(u);
    }
    if(m==n-1){
        ll ans=0;
        vector<ll>cnt(n+1,0);
        function <void(ll,ll)> dfs=[&](ll x,ll p){
            cnt[x]=1;
            for(auto y:adj[x]){
                if(y!=p){
                    dfs(y,x);
                    cnt[x]+=cnt[y];
                }
            }
            ans+=(cnt[x]-1)*(n-cnt[x])*2;
        };
        dfs(1,-1);
        cout<<ans;
    }
}

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