D

#include <bits/stdc++.h>

using namespace std;

#define ll     long long
#define _test   int _TEST; cin>>_TEST; while(_TEST--)
#define pb     push_back
#define ppb    pop_back


int main()
{
    _test
    {
        int n;
        cin>>n;

        vector<int> a(n);
        for(auto &e: a)
            cin>>e;

        sort(a.begin(), a.end());

        auto possible = [&](int x)
        {
            int i=0, j=0;

            while(j<n && (a[j]-a[i]+1)/2<=x)     j++;
            i = j;

            while(j<n && (a[j]-a[i]+1)/2<=x)     j++;
            i = j;

            while(j<n && (a[j]-a[i]+1)/2<=x)     j++;
            i = j;

            return (j == n);
        };

        int ans = 1e9;
        int low=0, high=1e9;

        while(low <= high)
        {
            int mid = (low+high)/2;

            if(possible(mid))
                ans=mid, high=mid-1;
            else
                low=mid+1;
        }


        cout<<ans<<"\n";
    }
}