제출 #30476

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
30476		sampriti	Network (BOI15_net)	C++14	63 / 100	516 ms	32100 KiB

net

#include <iostream>
#include <algorithm>
#include <vector>
#include <cassert>

using namespace std;

vector<int> G[500001];
vector<int> leaves;

void dfs(int i, int p) {
  bool leaf = true;

  for(int u: G[i]) {
    if(u == p) continue;

    leaf = false;
    dfs(u, i);
  }

  if(leaf) leaves.push_back(i);
}

int main() {
  ios::sync_with_stdio(false); cin.tie(0);

  int N; cin >> N;

  for(int i = 0; i < N - 1; i++) {
    int a, b; cin >> a >> b;
    G[a].push_back(b);
    G[b].push_back(a);
  }

  dfs(1, 0);
  if(G[1].size() == 1) leaves.push_back(1);

  int ans = (leaves.size() + 1)/2;

  cout << ans << endl;

  for(int i = 0; i < ans; i++) {
    assert((i + leaves.size()/2) < leaves.size());
    cout << leaves[i] << " " << leaves[i + leaves.size()/2] << endl;
  }
}

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