Submission #76788

#	Time	Username	Problem	Language	Result	Execution time	Memory
76788		shoemakerjo	Network (BOI15_net)	C++14	100 / 100	749 ms	72480 KiB

net

#include <bits/stdc++.h>

using namespace std;

#define maxn 500010
int n;
vector<vector<int>> adj(maxn);

vector<int> leaves;

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

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cin >> n;
	int a, b;
	for (int i = 0; i < n-1; i++) {
		cin >> a >> b;
		adj[a].push_back(b);
		adj[b].push_back(a);
	}
	for (int i = 1; i <= n; i++) {
		if (adj[i].size() != 1 || i == n) {
			dfs(i, -1);
			break;
		}
	}
	cout << (leaves.size()+1)/2 << endl;
	for (int i = 0; i + leaves.size()/2 < leaves.size(); i++) {
		cout << leaves[i] << " " << leaves[i + leaves.size()/2] << endl;
	}
	
}

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