Fragile network

input/code.cpp: In function 'int main()':
input/code.cpp:36:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   36 |     for (int i = 0; i < leafs.size() / 2; ++i) {
      |                     ~~^~~~~~~~~~~~~~~~~~

#include <iostream>
#include <vector>
#include <algorithm>
#include <stack>

int main() {
    int n;
    std::cin >> n;

    std::vector<std::vector<int>> edges(n);
    for (int i = 1; i < n; ++i) {
        int a, b;
        std::cin >> a >> b;
        edges[a-1].push_back(b-1);
        edges[b-1].push_back(a-1);
    }

    std::vector<int> leafs;

    std::stack<int> stack;
    stack.push(0);

    while(!stack.empty()) {
        int node = stack.top();
        stack.pop();

        if (edges[node].size() == 1) leafs.push_back(node);

        for (auto new_node : edges[node]) {
            if (node == new_node) continue;
            stack.push(new_node);
        }
    }

    std::cout << (leafs.size()+1) / 2 << std::endl;
    for (int i = 0; i < leafs.size() / 2; ++i) {
        std::cout << leafs[i] << " " << leafs[leafs.size()-1-i] << std::endl;
    }
    if (leafs.size() % 2 == 1) std::cout << leafs[0] << leafs[leafs.size()/2];
}

Test 1

Verdict: RUNTIME ERROR

Test 2

Verdict: TIME LIMIT EXCEEDED

Test 3

Verdict: TIME LIMIT EXCEEDED

Test 4

Verdict: TIME LIMIT EXCEEDED

Test 5

Verdict: TIME LIMIT EXCEEDED

Test 6

Verdict: RUNTIME ERROR

Test 7

Verdict: TIME LIMIT EXCEEDED

Test 8

Verdict: RUNTIME ERROR

Test 9

Verdict: TIME LIMIT EXCEEDED

Test 10

Verdict: TIME LIMIT EXCEEDED

Test 11

Verdict: TIME LIMIT EXCEEDED

Test 12

Verdict: TIME LIMIT EXCEEDED

Test 13

Verdict: TIME LIMIT EXCEEDED

Test 14

Verdict: TIME LIMIT EXCEEDED

Test 15

Verdict: TIME LIMIT EXCEEDED

Test 16

Verdict: TIME LIMIT EXCEEDED

Test 17

Verdict: TIME LIMIT EXCEEDED

Test 18

Verdict: TIME LIMIT EXCEEDED

Test 19

Verdict: TIME LIMIT EXCEEDED

Test 20

Verdict: TIME LIMIT EXCEEDED

Test 21

Verdict: TIME LIMIT EXCEEDED