Pair sort

input/code.cpp: In function 'int main()':
input/code.cpp:78:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   78 |     for (int i = 0; i < swaps.size(); i++)
      |                     ~~^~~~~~~~~~~~~~

// Online C++ compiler to run C++ program online
#include <iostream>
#include <vector>
#include <algorithm>
#include <unordered_map>

using namespace std;

int main() {
    int n;
    cin >> n;
    
    vector<int> nums(2 * n);
    vector<int> orig(2 * n);
    for (int i = 0; i < 2 * n; i++)
    {
        int t;
        cin >> t;
        nums[i] = t;
        orig[i] = t;
    }
    
    unordered_map<int, pair<int, int>> beforePosses;
    for (int i = 0; i < 2 * n; i++)
    {
        if (beforePosses.find(nums[i]) == beforePosses.end())
            beforePosses[nums[i]] = {i, -1};
        else
            beforePosses[nums[i]].second = i;
    }
    sort(nums.begin(), nums.end());
    
    vector<pair<int, int>> swaps;
    
    for (int i = 0; i < 2 * n; i += 2)
    {
        auto [p1, p2] = beforePosses[nums[i]];
        if (p1 > p2)
            swap(p1, p2);
            
        //cout << "They are at: " << p1 << " " << p2 << endl;
        
        if (i != p1)
        {
            swaps.push_back({i+1, p1+1});
            if (beforePosses[orig[i]].first == i)
            {
                //cout << "Changed " << beforePosses[orig[i]].first << " to " << p1;
                beforePosses[orig[i]].first = p1;
                orig[p1] = orig[i];
            }
            else if (beforePosses[orig[i]].second == i)
            {
                //cout << "Changed " << beforePosses[orig[i]].second << " to " << p1;
                beforePosses[orig[i]].second = p1;
                orig[p1] = orig[i];
            }
        }
        if (i + 1 != p2)
        {
            swaps.push_back({i+1+1, p2+1});
            if (beforePosses[orig[i + 1]].first == i + 1)
            {
                //cout << "Changed " << beforePosses[orig[i+1]].first << " to " << p2;
                beforePosses[orig[i + 1]].first = p2;
                orig[p2] = orig[i+1];
            }
            else if (beforePosses[orig[i + 1]].second == i + 1)
            {
                //cout << "Changed " << beforePosses[orig[i+1]].second << " to " << p2;
                beforePosses[orig[i + 1]].second = p2;
                orig[p2] = orig[i+1];
            }
        }
    }
    
    cout << swaps.size() << endl;
    for (int i = 0; i < swaps.size(); i++)
    {
        cout << swaps[i].first << " " << swaps[i].second << endl;
    }

    

    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