제출 #270511

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
270511		Hehehe	Network (BOI15_net)	C++14	100 / 100	601 ms	83952 KiB

net

#include<bits/stdc++.h> //:3
using namespace std;
typedef long long ll;
#define all(a) (a).begin(), (a).end()
#define ff first
#define ss second
#define pb push_back
#define mp make_pair
#define pi pair<int, int>
#define sz(x) (int)((x).size())
#define int long long

const int dx[] = {0, 1, 0, -1};
const int dy[] = {1, 0, -1, 0};

const ll inf = 2e9;
const ll mod = 1e9 + 7;
const int N = 2e6 + 11;
const ll INF64 = 3e18 + 1;
const double eps = 1e-14;
const double PI = acos(-1);

//ifstream in(".in");
//ofstream out(".out");

int n, m;
vector<int>v[N];
vector<int>leaves;

void dfs(int nod, int p){
    if(sz(v[nod]) == 1)leaves.push_back(nod);
    for(int it: v[nod]){
        if(it == p)continue;
        dfs(it, nod);
    }
}

void solve(){

    cin >> n;

    for(int i = 1, x, y; i < n; i++){
        cin >> x >> y;
        v[x].push_back(y);
        v[y].push_back(x);
    }

    dfs(1, 0);

    //cout << "L" << '\n';
    //for(auto it : leaves)cout << it << ' ';cout << '\n';

    int ans = (sz(leaves) + 1)/2;

    cout << ans << '\n';

    for(int i = 0; i < ans; i ++){
        cout << leaves[i] << ' ' << leaves[i + sz(leaves)/2] << '\n';
    }
}

int32_t main(){
    ios_base :: sync_with_stdio(0); cin.tie(0); cout.tie(0);
    int T = 1;
    //cin >> T;
    while(T--){
        solve();
    }
}

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