Submission #546669

#	Time	Username	Problem	Language	Result	Execution time	Memory
546669		Jomnoi	Network (BOI15_net)	C++17	100 / 100	401 ms	47676 KiB

net

#include <bits/stdc++.h>
#define DEBUG 0
using namespace std;

const int N = 5e5 + 10;

vector <int> adj[N];
vector <int> leaf;

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

int main() {
    cin.tie(0)->sync_with_stdio(0);
    int n;
    cin >> n;
    for(int i = 1; i <= n - 1; i++) {
        int a, b;
        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) {
            dfs(1, -1);
            break;
        }
    }

    cout << (leaf.size() + 1) / 2 << '\n';
    for(int i = 0; i < (leaf.size() + 1) / 2; i++) {
        cout << leaf[i] << ' ' << leaf[leaf.size() / 2 + i] << '\n';
    }
    return 0;
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:40:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   40 |     for(int i = 0; i < (leaf.size() + 1) / 2; i++) {
      |                    ~~^~~~~~~~~~~~~~~~~~~~~~~

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