Submission #1124610

#	Time	Username	Problem	Language	Result	Execution time	Memory
1124610		codexistent	Network (BOI15_net)	C++20	100 / 100	604 ms	46176 KiB

net

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define MAXN 500005
#define FOR(i, a, b) for(ll i = a; i <= b; i++)

ll n;
vector<ll> adj[MAXN], lvs;

void dfs(ll i, ll p){
    if(adj[i].size() == 1) lvs.push_back(i);

    for(ll i2 : adj[i]){
        if(i2 != p) dfs(i2, i);
    }
}

int main(){
    cin >> n;
    FOR(i, 1, n - 1){
        ll x, y;
        cin >> x >> y;
        adj[x].push_back(y), adj[y].push_back(x);
    }
    dfs(1, -1);

    cout << (lvs.size() + 1) / 2 << endl;
    FOR(i, 0, (lvs.size() + 1) / 2 - 1){
        cout << lvs[i] << " " << lvs[i + (lvs.size() / 2)] << endl;
    }
}

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