Submission #1112833

#	Time	Username	Problem	Language	Result	Execution time	Memory
1112833		Icelast	Network (BOI15_net)	C++17	100 / 100	304 ms	43996 KiB

net

#include <iostream>
#include <bits/stdc++.h>
#define ll long long
using namespace std;
const ll maxn = 2*1e5+5, INF = 4e18+9;
void solve(){
    int n;
    cin >> n;
    vector<vector<int>> adj(n+1);
    for(int i = 1; i < n; i++){
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    vector<int> leaf;
    auto dfs = [&](auto dfs, int u, int p) -> void{
        if(adj[u].size() == 1){
            leaf.push_back(u);
        }
        for(int v : adj[u]){
            if(v == p) continue;
            dfs(dfs, v, u);
        }
    };
    for(int i = 1; i <= n; i++){
        if(adj[i].size() > 1){
            dfs(dfs, i, 0);
            break;
        }
    }
    //leaf is sorted based on dfs order
    cout << (leaf.size()+1)/2 << "\n";
    for(int i = 0; i < leaf.size()/2; i++){
        cout << leaf[i] << " " << leaf[i+leaf.size()/2] << "\n";
    }
    if(leaf.size()&1){
        cout << leaf[0] << " " << leaf.back() << "\n";
    }
}
int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    solve();
}

Compilation message (stderr)

net.cpp: In function 'void solve()':
net.cpp:34:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   34 |     for(int i = 0; i < leaf.size()/2; i++){
      |                    ~~^~~~~~~~~~~~~~~

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