Submission #932596

#	Time	Username	Problem	Language	Result	Execution time	Memory
932596		vjudge1	Network (BOI15_net)	C++17	0 / 100	1 ms	512 KiB

net

// in the name of God
#include<bits/stdc++.h>
using namespace std;
#define int long long
#define fast() ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define ff first
#define ss second
#define pb(x) push_back(x)
#define all(x) x.begin(), x.end()
#define mk make_pair
#define ppb pop_back
#define endl '\n'
#define pii pair<int, int>
#define sz(x) (int)x.size()
#define file() freopen("input.txt", "r", stdin);
#pragma GCC optimize("Ofast")
#pragma GCC optimize("O4")
#pragma GCC optimize("unroll-loops")
//#pragma GCC target("avx2")
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int mod = 1e9 + 7, maxn = 2e3 + 10, sq = 3163, inf = 1e18 + 10, lg = 25, pp = 4447, modd = 1e9 + 9;

int n;
vector<vector<int>> g(maxn);
int h[maxn];

void dfs(int u = 0, int parr = -1){
	for(int v : g[u]){
		if(v != parr){
			h[v] = h[u] + 1;
			dfs(v, u);
		}
	}
}
bool cmp(int a, int b){
	if(h[a] > h[b]) return a > b;
	return a < b;
}
signed main(){
	fast();//file();
	cin >> n;
	for(int i = 1; i < n; ++i){
		int u, v; cin >> u >> v;
		u--; v--;
		g[u].pb(v);
		g[v].pb(u);
	}
	dfs();
	vector<int> b;
	for(int i = 0; i < n; ++i) if(g[i].size() == 1) b.pb(i);
	cout << ceil((double) b.size() / 2) << endl;
	sort(all(b), cmp);
	int p1 = 0, p2 = b.size() - 1;
	while(p1 < p2){
		cout << b[p1] + 1 << " " << b[p2] + 1 << endl;
		p1++;
		p2--;
	}
	if(b.size() % 2){
		cout << b[b.size() / 2] + 1 << " " << b.back() + 1;
	}
}
// Running from the daylight...

• Subtask 1: 0 / 18
• Subtask 2: 0 / 45
• Subtask 3: 0 / 37