Submission #529333

#	Time	Username	Problem	Language	Result	Execution time	Memory
529333		Alex_tz307	Network (BOI15_net)	C++17	100 / 100	419 ms	41860 KiB

net

#include <bits/stdc++.h>

using namespace std;

const int kN = 5e5;
vector<int> g[1 + kN], a;

void dfs(int u, int par) {
  if ((int)g[u].size() == 1) {
    a.emplace_back(u);
  }
  for (int v : g[u]) {
    if (v != par) {
      dfs(v, u);
    }
  }
}

/*
9
1 2
2 3
2 4
2 5
1 6
1 7
3 8
3 9
*/

void testCase() {
  int n;
  cin >> n;
  for (int i = 1; i < n; ++i) {
    int u, v;
    cin >> u >> v;
    g[u].emplace_back(v);
    g[v].emplace_back(u);
  }
  for (int v = 1; v <= n; ++v) {
    if ((int)g[v].size() > 1) {
      dfs(v, 0);
      break;
    }
  }
  int m = (a.size() + 1) / 2;
  cout << m << '\n';
  int k = a.size() / 2;
  for (int i = 0; i < m; ++i) {
    cout << a[i] << ' ' << a[(i + k) % a.size()] << '\n';
  }
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  int tests = 1;
  for (int tc = 0; tc < tests; ++tc) {
    testCase();
  }
  return 0;
}

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