Pair sort

#include <bits/stdc++.h>
using namespace std;
using ll = long long;

const int N = 2e5+1;
int A[N];
pair<int,int> V[N];

int main() {
  int n;
  cin >> n;
  for (int i = 1; i <= n*2; ++i) {
    cin >> A[i];
		V[A[i]] = {i,V[A[i]].first};
  }
	vector<pair<int,int>> ANS;
	for (int i = 1; i <= n*2; i += 2) {
		if (A[i] != A[i+1]) {
			int j = V[A[i]].first;
			ANS.push_back({i+1,j});
			auto [a,b] = V[A[i+1]];
			if (a == i+1) a = j;
			else b = j;
			if (a < b) swap(a,b);
			V[A[i+1]] = {a,b};
			swap(A[i+1],A[j]);
		}
	}
	cout << ANS.size() << '\n';
	for (auto [a,b] : ANS) {
		cout << a << ' ' << b << '\n';
	}
}

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