codeforce - constant palindromic sum

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define fast() (ios_base::sync_with_stdio(0),cin.tie(NULL))
int main()
{
    fast();
    ll t;
    cin>>t;
    while(t--)
    {
        ll n ,k;
        cin>>n>>k;
        ll ara[n+1],sub[2*k+1];
        for(ll i=0;i<n;i++)cin>>ara[i];
        for(ll i =0;i<=2*k;i++)sub[i]=0;
        for(ll i =0 ; i<n/2;i++)
        {
            sub[1]+=2;
            ll a= min(ara[i],ara[n-1-i]);
            ll b= max(ara[i],ara[n-1-i]);
            sub[a+1]--;
            sub[a+b]--;
            sub[a+b+1]++;
            sub[b+k+1]++;
        }
        ll cnt= 0, ans= 1e9;
        for(ll i =1;i<=2*k;i++)
        {
            cnt+=sub[i];
            //cout<<cnt<<endl;
            ans= min(cnt, ans);
        }
        cout<<ans<<endl;
    }
}