Pair sort

#include <bits/stdc++.h>

using namespace std;
#define ll long long

int main() {

    int n;
    cin >> n;

    vector<int> a(2*n);
    map<int, vector<int>> m;
    for (int i = 0; i < 2*n; i++) {
        int x;
        cin >> x;
        m[x].push_back(i);
        a[i] = x;
    }

    // cout << n << endl;

    vector<pair<int, int>> op;
    for (int i = 0; i < 2*n; i += 2) {
        if (a[i] == a[i+1]) continue;
        
        int u = i+1;
        int v = m[a[i]][1];
        
        op.push_back(make_pair(u, v));
        swap(m[a[u]][0], m[a[v]][1]);
        swap(a[u], a[v]);
        
    }

    cout << op.size() << endl;
    for (auto &[u, v] : op) cout << u+1 << " " << v+1 << endl;


}

Test 1

Verdict: ACCEPTED

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: 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