Submission #394607

#	Time	Username	Problem	Language	Result	Execution time	Memory
394607		amirmohammad_nezami	Network (BOI15_net)	C++14	100 / 100	531 ms	58824 KiB

net

//                                                          In the name of God 
//                                           We are everywhere while we are nowhere(Haj NEZAM...)
#include <bits/stdc++.h>
using namespace std;

#define F first
#define S second
#define lc 2 * v
#define rc 2 * v + 1
#define PB push_back
#define MP make_pair
#define ll long long
#define int long long
#define ld long double
#define mid (s + e) / 2
#define pii pair <int , int>
#define _sz(e) (int)e.size()
#define _all(e) e.begin() , e.end()
#define pll pair <long long , long long>
#define piii pair <int , pair <int , int> >
#define FAST ios::sync_with_stdio(0);cin.tie(0)
#define UNI(e) e.resize(unique(_all(e)) - e.begin())

#define kill(e) cout << e << '\n'

#pragma GCC optimize ("O3")
#pragma GCC optimize ("unroll-loops")

const int maxn = 5e5 + 5 , N = 1e6 + 5 , SQ = 450 , base = 800287 , mod = 1e9 + 7 , INF = 1e9 + 5 , lg = 20;
const ld eps = 1e-4;

int n , root;
vector <int> vec;
vector <int> edges[maxn];

void dfs(int v , int p = -1) {
	if(_sz(edges[v]) == 1) {
		vec.PB(v);
	}

	for (auto u : edges[v]) {
		if(u != p) {
			dfs(u , v);
		}
	}
}

int32_t main() {
	FAST;
	cin >> n;
	for (int i = 0; i < n - 1; ++i) {
		int x , y; cin >> x >> y;
		x-- , y--;
		edges[x].PB(y);
		edges[y].PB(x);
	}
	for (int i = 0; i < n; ++i) {
		if(_sz(edges[i]) > 1) {root = i;}
	}
	dfs(root);
	
	int ans = (_sz(vec) + 1) / 2;
	cout << ans << '\n';
	for (int i = 0; i < ans; ++i) {
		int nxt = min(_sz(vec) - 1 , i + ans);
		cout << vec[i] + 1 << ' ' << vec[nxt] + 1 << '\n';
	}
}
 // Mistakes:
//  * Read the problem carefully.
//  * Check maxn.
//  * Overflows.

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