Submission #1166823

#	Time	Username	Problem	Language	Result	Execution time	Memory
1166823		CrabCNH	Network (BOI15_net)	C++20	100 / 100	167 ms	46164 KiB

net

#include <bits/stdc++.h>

#define task   "BriantheCrab"

#define int    long long
#define pii    pair <int, int>
#define fi     first
#define se     second
#define szf    sizeof
#define sz(s)  (int)((s).size())

using namespace std;

template <class T> void mini (T &t, T f) {if (t > f) t = f;}
template <class T> void maxi (T &t, T f) {if (t < f) t = f;}

const int maxN = 5e5 + 5;
const int inf = 1e18 + 7;
const int mod = 1e9 + 7;

vector <int> adj[maxN], leaves;

void dfs (int u, int p) {
    if (adj[u].size () == 1) {
        leaves.push_back (u);        
    }
    for (auto v : adj[u]) {
        if (v != p) {
            dfs (v, u);
        }
    }
}

void solve () {
    int n;
    cin >> n;
    for (int i = 1; i <= n - 1; i ++) {
        int u, v;
        cin >> u >> v;
        adj[u].push_back (v);
        adj[v].push_back (u);
    }
    int rt = 1;
    for (int i = 1; i <= n; i ++) {
        if (adj[i].size () >= 2) {
            rt = i;
            break;
        }
    }
    dfs (rt, rt);
    int l = leaves.size ();
    cout << (l + 1) / 2 << '\n';
    for (int i = 0; i < (l + 1) / 2; i ++) {
        cout << leaves[i] << ' ' << leaves[(i + l / 2) % l] << '\n';
    }
    return;
}

signed main () {
    cin.tie (nullptr) -> sync_with_stdio (false);
    if (fopen (task".inp", "r")) {
        freopen (task".inp", "r", stdin);
        freopen (task".out", "w", stdout);
    }
    int t = 1;
    //cin >> t;
    while (t --) {
        solve ();
    } 
    return 0;
}
// thfdgb

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:62:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   62 |         freopen (task".inp", "r", stdin);
      |         ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
net.cpp:63:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   63 |         freopen (task".out", "w", stdout);
      |         ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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