Submission #755839

#	Time	Username	Problem	Language	Result	Execution time	Memory
755839		JellyTheOctopus	Network (BOI15_net)	C++17	100 / 100	672 ms	51940 KiB

net

// Baltic Olympiad in Informatics 2015 Day 1 Problem 3
// Network
// https://oj.uz/problem/view/BOI15_net

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

int N;
vector<int> adjList[500001];
vector<int> leaf;

void DFS(int node, int parent) {
	int numOfVertices = 0;
	for (auto child: adjList[node]) {
		numOfVertices++;
		if (child != parent) {
			DFS(child, node);
		}
	}
	if (numOfVertices == 1) {
		leaf.push_back(node);
	}
}

int main() {
	cin >> N;
	for (int i = 1; i < N; i++) {
		int u, v;
		cin >> u >> v;
		adjList[u].push_back(v);
		adjList[v].push_back(u);
	}
	DFS(1, -1);
	int k = (int)leaf.size();
	if (k % 2 == 0) {
		cout << k/2 << "\n";
		for (int i = 0; i < k/2; i++) {
			cout << leaf[i] << " " << leaf[i+k/2] << "\n";
		}
	}
	else {
		cout << k/2+1 << "\n";
		for (int i = 0; i < k/2; i++) {
			cout << leaf[i] << " " << leaf[i+k/2+1] << "\n";
		}
		cout << leaf[k/2] << " " << 1 << "\n";
	}
}

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