Pair sort

#include <cstdio>
#include <iostream>
#include <utility>
#include <vector>

using namespace std;

int main(int argc, char *argv[])
{
	// Read the input parameters
	int n;
	cin >> n;

	// Read values from one line
    vector<int> occurence(n + 1, -1);
	vector<int> input_line(2*n);
	for (int i = 0; i < 2 * n; i++) {
        int tmp;
		cin >> tmp;
        if (occurence[tmp] == -1) {
            occurence[tmp] = i;
        }
        input_line[i] = tmp;
	}

    // for (int i = 0; i < n + 1; i++) {
    //     cout << occurence[i] << " ";
    // }
    // cout << "\n";
    vector<pair<int, int>> swaps;
    int swaps_amount = 0;
    for (int i = 2*n - 1; i > 1; i -= 2) {
        if (input_line[i] == input_line[i-1]) continue;
        else {
            int og_value = input_line[i];
            // cout << input_line[i-1] << " ";
            int first_index = occurence[input_line[i-1]];
            // cout << input_line[i] << "\n";
            // swap to match the pair
            swaps.push_back({i + 1, first_index + 1});
            swaps_amount++;
            // int tmp = input_line[i];
            input_line[first_index] = input_line[i];
            input_line[i] = input_line[i-1];
            // update the first location of i
            // cout << input_line[i] << " " << occurence[input_line[i]] << "\n";
            if (occurence[og_value] > first_index) {
                occurence[og_value] = first_index;
            }
        }
    }

    cout << swaps_amount << "\n";
    for (int i = 0; i < swaps_amount; i++) {
        cout << swaps[i].first << " " << swaps[i].second << "\n";
    }

    // for (int i = 0; i < n + 1; i++) {
    //     cout << occurence[i] << " ";
    // }
    // cout << "\n";

	return 0;
}

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