Submission #1263566

#	Time	Username	Problem	Language	Result	Execution time	Memory
1263566		dzhoz0	Network (BOI15_net)	C++20	100 / 100	285 ms	50456 KiB

net

#include <bits/stdc++.h>
using namespace std;

#define int long long
#define INF 1e18
#define f first
#define s second
#define pii pair<int, int>
#define vi vector<int>

const int MOD = 1'000'000'000 + 7;

void setIO(string name = "")
{
    ios_base::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);
#ifdef LOCAL
    freopen("inp.txt", "r", stdin);
    freopen("out.txt", "w", stdout);
#else
    if (!name.empty())
    {
        freopen((name + ".INP").c_str(), "r", stdin);
        freopen((name + ".OUT").c_str(), "w", stdout);
    }
#endif
}

const int MAXN = 5e5;
int n;
vi g[MAXN + 5];
vi leaves;

void dfs(int u, int par) {
    int cnt = 0;
    for(int v : g[u]) {
        if(v == par) continue;
        dfs(v, u);
        cnt++;
    }
    if(cnt == 0 || g[u].size() == 1) leaves.push_back(u);
}

void solve()
{
    cin >> n;
    for(int i = 1; i < n; i++) {
        int u, v; cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }

    dfs(1, 1);

    cout << ((int)leaves.size() + 1) / 2 << '\n';

    for(int i = 0; i < (int)leaves.size() / 2; i++) {
        cout << leaves[i] << ' ' << leaves[(int)leaves.size() / 2 + i] << '\n';
    }

    if((int)leaves.size() & 1) cout << leaves.back() << ' ' << leaves[0] << '\n';

}
signed main()
{
    setIO();
    int t = 1;
    // cin >> t;
    while (t--)
        solve();
}

Compilation message (stderr)

net.cpp: In function 'void setIO(std::string)':
net.cpp:23:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   23 |         freopen((name + ".INP").c_str(), "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
net.cpp:24:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   24 |         freopen((name + ".OUT").c_str(), "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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