Submission #71441

#	Time	Username	Problem	Language	Result	Execution time	Memory
71441		Googal	Network (BOI15_net)	C++14	100 / 100	792 ms	155572 KiB

net

#include <iostream>
#include <vector>

using namespace std;

const int NMAX = 6 * 1e5 + 1e2;

int n;
int startn;

vector < int > g[1 + NMAX];
vector < int > res;

void dfs(int u, int v) {
  if(g[u].size() == 1) {
    res.push_back(u);
    return;
  }

  for(int i = 0; i < g[u].size(); i++) {
    if(g[u][i] == v)
      continue;
    dfs(g[u][i], u);
  }
}

int main()
{
  ios::sync_with_stdio(false);

  cin >> n;
  for(int i = 1; i < n; i++) {
    int x, y;
    cin >> x >> y;

    g[x].push_back(y);
    g[y].push_back(x);
  }

  for(int i = 1; i <= n; i++) {
    if(g[i].size() >= 2) {
      startn = i;
      break;
    }
  }

  dfs(startn, -1);

  int rsize = res.size();

  cout << rsize / 2 + rsize % 2 << '\n';
  for(int i = 0; i + rsize / 2 < rsize; i++)
    cout << res[i] << ' ' << res[i + rsize / 2] << '\n';

  return 0;
}

Compilation message (stderr)

net.cpp: In function 'void dfs(int, int)':
net.cpp:20:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i = 0; i < g[u].size(); i++) {
                  ~~^~~~~~~~~~~~~

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