#pragma GCC target("avx")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include<bits/stdc++.h>
// #include<ext/pb_ds/assoc_container.hpp>
// #include<ext/pb_ds/tree_policy.hpp>
// #include<ext/pb_ds/tag_and_trait.hpp>
// using namespace __gnu_pbds;
// #include<boost/multiprecision/cpp_int.hpp>
// namespace multiprecisioninteger = boost::multiprecision;
// using cint=multiprecisioninteger::cpp_int;
using namespace std;
using ll=long long;
using datas=pair<ll,ll>;
using ddatas=pair<long double,long double>;
using tdata=pair<ll,datas>;
using vec=vector<ll>;
using mat=vector<vec>;
using pvec=vector<datas>;
using pmat=vector<pvec>;
// using llset=tree<ll,null_type,less<ll>,rb_tree_tag,tree_order_statistics_node_update>;
#define For(i,a,b) for(i=a;i<(ll)b;++i)
#define bFor(i,b,a) for(i=b,--i;i>=(ll)a;--i)
#define rep(i,N) For(i,0,N)
#define rep1(i,N) For(i,1,N)
#define brep(i,N) bFor(i,N,0)
#define brep1(i,N) bFor(i,N,1)
#define all(v) (v).begin(),(v).end()
#define allr(v) (v).rbegin(),(v).rend()
#define vsort(v) sort(all(v))
#define vrsort(v) sort(allr(v))
#define uniq(v) vsort(v),(v).erase(unique(all(v)),(v).end())
#define endl "\n"
#define popcount __builtin_popcountll
#define eb emplace_back
#define print(x) cout<<x<<endl
#define printyes print("Yes")
#define printno print("No")
#define printYES print("YES")
#define printNO print("NO")
#define output(v) do{bool f=0;for(auto outi:v){cout<<(f?" ":"")<<outi;f=1;}cout<<endl;}while(0)
#define matoutput(v) do{for(auto outimat:v)output(outimat);}while(0)
// constexpr ll mod=1000000007;
constexpr ll mod=998244353;
constexpr ll inf=1LL<<60;
constexpr long double eps=1e-9;
const long double PI=acosl(-1);
template<class T,class E> ostream& operator<<(ostream& os,const pair<T,E>& p){return os<<"("<<p.first<<","<<p.second<<")";}
template<class T> ostream& operator<<(ostream& os,const vector<T>& v){
  os<<"{";bool f=false;
  for(auto& x:v){if(f)os<<",";os<<x;f=true;}
  os<<"}";
  return os;
}
template<class T> ostream& operator<<(ostream& os,const set<T>& v){
  os<<"{";bool f=false;
  for(auto& x:v){if(f)os<<",";os<<x;f=true;}
  os<<"}";
  return os;
}
template<class T> ostream& operator<<(ostream& os,const multiset<T>& v){
  os<<"{";bool f=false;
  for(auto& x:v){if(f)os<<",";os<<x;f=true;}
  os<<"}";
  return os;
}
template<class T,class E> ostream& operator<<(ostream& os,const map<T,E>& v){
  os<<"{";bool f=false;
  for(auto& x:v){if(f)os<<",";os<<x;f=true;}
  os<<"}";
  return os;
}
template<class T> inline bool chmax(T& a,const T b){bool x=a<b;if(x)a=b;return x;}
template<class T> inline bool chmin(T& a,const T b){bool x=a>b;if(x)a=b;return x;}
#ifdef DEBUG
void debugg(){cout<<endl;}
template<class T,class... Args>void debugg(const T& x,const Args&... args){cout<<" "<<x;debugg(args...);}
#define debug(...) cout<<__LINE__<<" ["<<#__VA_ARGS__<<"]:",debugg(__VA_ARGS__)
#else
#define debug(...) (void(0))
#endif

inline void startupcpp(void) noexcept{
  cin.tie(0);
  ios::sync_with_stdio(false);
}

struct mex{
  int sz=1,ans=0;
  vector<int> v,lis;
  mex(){};
  mex(vector<int> v){
    sz=v.size();
    for(auto x:v)insert(x);
  }
  void insert(int x){
    v.resize(sz,0);
    if(x<sz)++v[x];
    else lis.emplace_back(x);
    if(x==ans){
      while(ans<sz&&v[ans])++ans;
      if(ans==sz){
        v.resize(sz<<=1);
        vector<int> slis=lis;
        lis.clear();
        for(auto x:slis)insert(x);
      }
    }
  }
  int calc(){
    return ans;
  }
};
void solve(){
  int i,N;
  cin>>N;
  vector<int> p(N);
  rep(i,N){
    cin>>p[i];
    p[i]--;
  }
  {
    mex t;
    rep(i,N){
      t.insert(p[i]);
      if(i==p[i]&&t.calc()!=i+1){
        print(-1);
        return;
      }
    }
  }
  vector<int> ans;
  rep(i,N){
    if(i==p[i])continue;
    int j=i;
    while(i!=p[j]){
      assert(j<N&&p[j]!=j);
      ++j;
    }
    while(i<j){
      assert(p[j]==i);
      if(p[j-1]!=j){
        ans.emplace_back(j);
        swap(p[j-1],p[j]);
        --j;
        continue;
      }
      int k=j-1;
      while(i<=k&&p[k]==k+1)--k;
      if(k==i-1){
        while(i<j){
          ans.emplace_back(j);
          swap(p[j-1],p[j]);
          --j;
        }
        break;
      }
      while(k<j){
        ans.emplace_back(k+1);
        swap(p[k],p[k+1]);
        ++k;
      }
      --j;
      continue;
    }
    assert(p[i]==i);
  }
  print(ans.size());
  output(ans);
}
int main(){
  startupcpp();
  ll T;
  cin>>T;
  while(T--)solve();
}