Submission #1202617

#	Time	Username	Problem	Language	Result	Execution time	Memory
1202617		Gray	Network (BOI15_net)	C++20	0 / 100	0 ms	324 KiB

net

#include <algorithm>
#include <bits/stdc++.h>
#include <cassert>
using namespace std;
#define ll long long
#define ff first
#define ss second
#define ln "\n"
const ll MOD = 998244353;
const ll INF = 2e18;

void dfs(ll u, ll p, vector<vector<ll>> &A, vector<ll> &lf){
    for (auto v:A[u]){
        if (v==p) continue;
        dfs(v, u, A, lf);
    }
    if (A[u].size()==1) lf.push_back(u);
}

void solve(){
    ll n; cin >> n;
    vector<vector<ll>> A(n);
    for (ll i=0; i<n-1; i++){
        ll u, v; cin >> u >> v; u--; v--;
        A[u].push_back(v); A[v].push_back(u);
    }
    vector<ll> lf; dfs(1, 1, A, lf);
    vector<pair<ll, ll>> e;
    for (ll i=2; i<(ll)lf.size(); i++){
        e.push_back({lf[i-2], lf[i]});
    }
    if (lf.size()<=3) e.push_back({lf[1], lf[0]});
    cout << e.size() << ln;
    for (auto ch:e) cout << ch.ff+1 << " " << ch.ss+1 << ln;

}

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

• Subtask 1: 0 / 18
• Subtask 2: 0 / 45
• Subtask 3: 0 / 37