https://codeforces.com/contest/1561/problem/B

#include <bits/stdc++.h>

using namespace std;

int main() {
  int tt;
  cin >> tt;
  while (tt–) {
    int n;
    cin >> n;
    vector<int> a(n);
    for (int i = 0; i < n; i++) {
      cin >> a[i];
    }
    int ans = 0;
    while ( ! is_sorted(a.begin(), a.end()  )) ///////////返回是否为补递减序列
    {
      for (int i = ans % 2; i + 1 < n; i += 2) {
        if (a[i] > a[i + 1]) {
          swap(a[i], a[i + 1]);
        }
      }
      ans += 1;
    }
    cout << ans << endl;
  }
  return 0;
}