Submission #547970

#	Time	Username	Problem	Language	Result	Execution time	Memory
547970		Soumya1	Network (BOI15_net)	C++17	100 / 100	476 ms	53932 KiB

net

#include <bits/stdc++.h>
#ifdef __LOCAL__
#include <debug_local.h>
#endif
using namespace std;
const int mxN = 5e5 + 5;
vector<int> ad[mxN];
int in[mxN];
vector<int> leafs;
int timer;
void dfs(int u, int p) {
  int childs = 0;
  in[u] = ++timer;
  for (int v : ad[u]) {
    if (v == p) continue;
    dfs(v, u);
    childs++;
  }
  if (!childs) {
    leafs.push_back(u);
  }
}
void testCase() {
  int n;
  cin >> n;
  for (int i = 1; i < n; i++) {
    int u, v;
    cin >> u >> v;
    ad[u].push_back(v);
    ad[v].push_back(u);
  }
  for (int i = 1; i <= n; i++) {
    if ((int) ad[i].size() > 1) {
      dfs(i, -1);
      break;
    }
  }
  sort(leafs.begin(), leafs.end(), [&](int i, int j) { return in[i] < in[j]; });
  cout << (int) (leafs.size() + 1) / 2 << "\n";
  for (int i = 0; i < (int) (leafs.size() + 1) / 2; i++) {
    int j = (int) leafs.size() / 2 + i;
    cout << leafs[i] << " " << leafs[j] << "\n";
  }
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  testCase();
  return 0;
}

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