Pair sort

#include <iostream>
#include <vector>
#include <algorithm>
#include <cstdint>
#include <limits>
#include <utility>

int main() {
    int64_t n;
    std::cin >> n;
    
    std::vector<int64_t> array(2*n);
    for (auto &element : array) {
        std::cin >> element;
    }

    std::vector<std::pair<int, int>> swaps;

    std::vector<int64_t> indicies(n+1, -1);
    for (int64_t i = 0; i < 2*n; ++i) {
        int64_t element = array[i];
        if (indicies[element] == -1) {
            indicies[element] = i;
        } else {
            int64_t new_position = indicies[element];
            if (new_position%2 == 1) new_position--;
            else new_position++;

            if (new_position == i) continue;

            int64_t old_element = array[new_position];
            indicies[old_element] = i;

            std::swap(array[i], array[new_position]);
            swaps.push_back({new_position, i});
        }
    }

    std::cout << swaps.size() << std::endl;
    for (auto &swap : swaps) {
        std::cout << swap.first+1 << " " << swap.second+1 << std::endl;
    }
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED