Submission #1184852

#	Time	Username	Problem	Language	Result	Execution time	Memory
1184852		qrn	Network (BOI15_net)	C++20	100 / 100	385 ms	46168 KiB

net

#include <bits/stdc++.h>
// #include <ext/pb_ds/assoc_container.hpp>
using namespace std;
// using namespace __gnu_pbds;

#define SPEED                     \
    ios_base::sync_with_stdio(0); \
    cin.tie(NULL);                \
    cout.tie(NULL);

#define pb push_back
#define ins insert
#define fi first
#define se second

#define endl "\n"
#define ALL(x) x.begin(), x.end()
#define sz(x) x.size()
#define intt long long

const intt mod = 1e9 + 7;
const intt base = 31;
const intt inf = 1e9;
const intt mxN = 2e5 + 5;
const intt L = 21;

vector<vector<intt>> graph;
vector<intt> v;

void dfs(intt node, intt parent) {
    if(graph[node].size() == 1) {
        v.pb(node);
    }

    for(auto u : graph[node]) {
        if(u != parent){
            dfs(u, node);
        }
    }
}

void solve() {
    intt N;
    cin >> N;

    graph.assign(N + 1, vector<intt> {});
    for(intt i = 0; i < N - 1; i++) {
        intt a, b;
        cin >> a >> b;
        graph[a].pb(b);
        graph[b].pb(a);
    }

    dfs(1, 1);
    cout << v.size() / 2 + (v.size() % 2 != 0) << endl;
    intt l = 0, r = v.size() - 1;
    while(l < v.size() / 2) {
        cout << v[l] << " " << v[l+v.size()/2] << endl;
        l++; 
    }
    if(v.size() % 2 != 0) {
        cout << v[0] << " " << v.back() << endl;
    }
}

signed main() {
    SPEED;
    intt tst = 1;
    // cin >> tst;
    while (tst--) {
        solve();
    }
}

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