Submission #227999

#	Time	Username	Problem	Language	Result	Execution time	Memory
227999		quocnguyen1012	Network (BOI15_net)	C++14	100 / 100	551 ms	69496 KiB

net

#include <bits/stdc++.h>

#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define ar array

using namespace std;
typedef long long ll;
typedef pair<int, int> ii;

const int maxn = 5e5 + 5;

int deg[maxn], N;
vector<int> leaf;
vector<int> adj[maxn];
int sz[maxn];

void dfs(int u, int p = -1)
{
  sz[u] = 1;
  for(int v : adj[u]) if(v != p){
    dfs(v, u);
    sz[u] += sz[v];
  }
  if(sz[u] == 1) leaf.eb(u);
}

signed main(void)
{
  ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  #ifdef LOCAL
    freopen("A.INP", "r", stdin);
    freopen("A.OUT", "w", stdout);
  #endif // LOCAL
  cin >> N;
  for(int i = 1; i < N; ++i){
    int u, v; cin >> u >> v;
    deg[u]++; deg[v]++;
    adj[u].eb(v); adj[v].eb(u);
  }
  int r;
  for(int i = 1; i <= N; ++i)
    if(adj[i].size() >= 2) r = i;
  dfs(r);
  cout << (leaf.size() + 1) / 2 << '\n';
  int half = leaf.size() / 2;
  for(int i = 0; i <= (leaf.size() - 1) / 2; ++i)
    cout << leaf[i] << ' ' << leaf[i + half] << '\n';
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:50:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i = 0; i <= (leaf.size() - 1) / 2; ++i)
                  ~~^~~~~~~~~~~~~~~~~~~~~~~~
net.cpp:47:6: warning: 'r' may be used uninitialized in this function [-Wmaybe-uninitialized]
   dfs(r);
   ~~~^~~

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