Fragile network

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

#define int long long

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

const int N = 1e5 + 5;

int n;
vector<int> adj[N];
vector<int> leaves;

void dfs(int u, int p) {
    int cnt = 0;
    for (int v : adj[u]) {
        if (v == p) continue;
        cnt++;
        dfs(v, u);
    }
    if (cnt == 0 || (cnt == 1 && p == 0)) leaves.push_back(u);
}

signed main() {
    cin.tie(0)->sync_with_stdio(0);
    cin.exceptions(cin.failbit); // RTE if input wrong datatype

    cin >> n;
    for (int i = 1; i < n; i++) {
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }

    dfs(1, 0);

    cout << sz(leaves) - 1 << '\n';
    for (int i = 1; i < sz(leaves); i++) {
        cout << leaves[0] << ' ' << leaves[i] << '\n';
    }
}

Test 1

Verdict: WRONG ANSWER

Test 2

Verdict: ACCEPTED

Test 3

Verdict: WRONG ANSWER

Test 4

Verdict: WRONG ANSWER

Test 5

Verdict: WRONG ANSWER

Test 6

Verdict: WRONG ANSWER

Test 7

Verdict: ACCEPTED

Test 8

Verdict: WRONG ANSWER

Test 9

Verdict: WRONG ANSWER

Test 10

Verdict: WRONG ANSWER

Test 11

Verdict: WRONG ANSWER

Test 12

Verdict: WRONG ANSWER

Test 13

Verdict: WRONG ANSWER

Test 14

Verdict: WRONG ANSWER

Test 15

Verdict: WRONG ANSWER

Test 16

Verdict: WRONG ANSWER

Test 17

Verdict: WRONG ANSWER

Test 18

Verdict: WRONG ANSWER

Test 19

Verdict: WRONG ANSWER

Test 20

Verdict: WRONG ANSWER

Test 21

Verdict: WRONG ANSWER