Submission #1164498

#	Time	Username	Problem	Language	Result	Execution time	Memory
1164498		Nonoze	Network (BOI15_net)	C++20	100 / 100	190 ms	58940 KiB

net

/*
*	Author: Nonoze
*	Created: Sunday 09/03/2025
*/
#include <bits/stdc++.h>
using namespace std;

#ifndef DEBUG
	#define dbg(...)
#endif

// #define cout cerr << "OUT: "
#define endl '\n'
#define endlfl '\n' << flush
#define quit(x) return (void)(cout << x << endl)

template<typename T> void read(T& x) { cin >> x;}
template<typename T1, typename T2> void read(pair<T1, T2>& p) { read(p.first), read(p.second);}
template<typename T> void read(vector<T>& v) { for (auto& x : v) read(x); }
template<typename T1, typename T2> void read(T1& x, T2& y) { read(x), read(y); }
template<typename T1, typename T2, typename T3> void read(T1& x, T2& y, T3& z) { read(x), read(y), read(z); }
template<typename T1, typename T2, typename T3, typename T4> void read(T1& x, T2& y, T3& z, T4& zz) { read(x), read(y), read(z), read(zz); }
template<typename T> void print(vector<T>& v) { for (auto& x : v) cout << x << ' '; cout << endl; }

#define sz(x) (int)(x.size())
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define make_unique(v) sort(all(v)), v.erase(unique(all(v)), (v).end())
#define pb push_back
#define mp(a, b) make_pair(a, b)
#define fi first
#define se second
#define cmin(a, b) a = min(a, b)
#define cmax(a, b) a = max(a, b)
#define YES cout << "YES" << endl
#define NO cout << "NO" << endl
#define QYES quit("YES")
#define QNO quit("NO")

#define int long long
#define double long double
const int inf = numeric_limits<int>::max() / 4;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int MOD = 1e9+7, LOG=20;



void solve();

signed main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	int tt=1;
	// cin >> tt;
	while(tt--) solve();
	return 0;
}




int n, k, m, q;
vector<vector<int>> adj;
vector<int> leaves;

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


void solve() {
	read(n);
	adj.clear(), adj.resize(n);
	for (int i=1; i<n; i++) {
		int u, v; read(u, v); u--, v--;
		adj[u].pb(v), adj[v].pb(u);
	}
	int root=0; for (int i=0; i<n; i++) if (sz(adj[i])>1) root=i;
	dfs(root);
	cout << (sz(leaves)+1)/2 << endl;
	for (int i=0; i<(sz(leaves)+1)/2; i++) cout << leaves[i]+1 << ' ' << leaves[(i+sz(leaves)/2)%sz(leaves)]+1 << endl;
}

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