Vaihdot

#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int T;
  cin >> T;
  for (int Ti = 0; Ti < T; ++Ti) {
    int n;
    cin >> n;
    int t[n];
    for (int i = 0; i < n; ++i) cin >> t[i];
    if (n == 2) {
      cout << (t[0] == 1 ? 0 : -1) << endl;
      continue;
    }
    if (n == 3) {
      if (t[1] != 2) {
        cout << -1 << endl;
      } else if (t[0] != 1) {
        cout << "1\n1 3\n";
      } else {
        cout << "0\n";
      }
      continue;
    }
    vector<pair<int, int>> res;
    for (int a = 0; a < n; ++a) {
      if (t[a] == a+1) continue;
      int b;
      for (int j = a+1; j < n; ++j) {
        if (t[j] == a+1) {
          b = j;
          break;
        }
      }
      swap(t[a], t[b]);
      if (a > b) swap(a, b);
      if (b == a+1) {
        if (a > 1) {
          res.emplace_back(0, b);
          res.emplace_back(0, a);
          res.emplace_back(0, b);
        } else if (b < n-2) {
          res.emplace_back(b, n-1);
          res.emplace_back(a, n-1);
          res.emplace_back(b, n-1);
        } else {
          res.emplace_back(1, 3);
          res.emplace_back(0, 2);
          res.emplace_back(0, 3);
          res.emplace_back(1, 3);
          res.emplace_back(0, 2);
        }
      } else {
        res.emplace_back(a, b);
      }
    }
    cout << res.size() << endl;
    for (auto [a, b] : res) cout << a+1 << " " << b+1 << endl;
  }
}

Test 1

Subtask: 1, 2

Verdict: ACCEPTED

Test 2

Subtask: 2

Verdict: ACCEPTED