Pair sort

#include <bits/stdc++.h>

using namespace std;
#define int long long

// g++ <filename>.cpp -g -Wall -Wextra -DDEBUG -o <executable>

// copied from: https://codeforces.com/blog/entry/79024
// === Debug macro starts here ===

int recur_depth = 0;
#ifdef DEBUG
#define dbg(x) {++recur_depth; auto x_=x; --recur_depth; cerr<<string(recur_depth, '\t')<<"\e[91m"<<__func__<<":"<<__LINE__<<"\t"<<#x<<" = "<<x_<<"\e[39m"<<endl;}
#else
#define dbg(x)
#endif
template<typename Ostream, typename Cont>
typename enable_if<is_same<Ostream,ostream>::value, Ostream&>::type operator<<(Ostream& os,  const Cont& v){
	os<<"[";
	for(auto& x:v){os<<x<<", ";}
	return os<<"]";
}
template<typename Ostream, typename ...Ts>
Ostream& operator<<(Ostream& os,  const pair<Ts...>& p){
	return os<<"{"<<p.first<<", "<<p.second<<"}";
}

// === Debug macro ends here ===

signed main() {
    
    int n;
    cin >> n;

    vector<int> positions(2*n+1, -1); // saved indices
    vector<vector<int>> swap_list;

    int swaps = 0;

    for (int i = 1; i < 2*n; i++) {
        
        int number;
        cin >> number;

        if (positions[number] == -1) { // first encounter of number
            positions[number] = i;
        } else { // second encounter of number

            swaps++;
            vector<int> swap_numbers; 

            if (positions[number] % 2 != 0) { // odd index, swap after number
                swap_numbers = {positions[number] + 1, i};

                // update

            } else {
                swap_numbers = {positions[number] - 1 , i};                

                // update

            }

            swap_list.push_back(swap_numbers);
        }


    }

    cout << swaps << "\n";
    
    for (auto s : swap_list) {
        cout << s[0] << " " << s[1] << "\n";
    }
    
    

    return 0;
}

Test 1

Verdict: WRONG ANSWER

Test 2

Verdict: WRONG ANSWER

Test 3

Verdict: WRONG ANSWER

Test 4

Verdict: WRONG ANSWER

Test 5

Verdict: WRONG ANSWER

Test 6

Verdict: WRONG ANSWER

Test 7

Verdict: WRONG ANSWER

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