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#include <bits/stdc++.h>
#define all(vec) vec.begin(),vec.end()
#define CLR(i,a) memset(i,a,sizeof(i))
#define fi first
#define se second
#define pb push_back
#define SZ(a) ((int) a.size())
#define FOR(i, a, b) for (int i = (a); i <= (b); ++i)
#define ROF(i, a, b) for (int i = (a); i >= (b); --i)
#define debug(var) cerr << #var <<":"<<var<<"\n";
#define lson(var) (var<<1)
#define rson(var) ((var<<1)+1)
using namespace std;
typedef long long ll;typedef unsigned long long ull;
typedef double DB;typedef long double LD;
typedef __int128 i128;typedef pair<DB,DB> pdd;typedef pair<ll,bool> plb;
typedef pair<ll,ll> pll;
typedef array<ll,3> arr3;typedef array<ll,2> arr2;
constexpr ll MAXN=static_cast<ll>(1e6)+10,INF=static_cast<ll>(1e9)+9;
constexpr ll mod=static_cast<ll>(1e9)+7;
constexpr double eps=1e-8;
ll N,M,Q,X,K,lT,A[MAXN];
inline void init(){
}
inline ll diff(ll a,ll b){
if(a<=b) return 0;
bitset<32> ba(a);
bitset<32> bb(b);
ROF(i,31,0){
ll bai=ba[i],bbi=bb[i];
if(bai-bbi==1){
return 1<<i;
}
}
}
inline void solve(){
cin>>N;
init();
FOR(i,1,N){
cin>>A[i];
}
bool isSort=true;
FOR(i,2,N){
if(A[i-1]>A[i]){isSort=false;break;}
}
if(isSort){cout<<0<<"\n";return;}
ll mxD=0,mx=A[1];
FOR(i,2,N){
mxD=max(mxD,diff(mx,A[i]));
mx=max(mx,A[i]);
}
cout<<mxD<<"\n";
}
int main()
{
ios::sync_with_stdio(false);
cin.tie(0);cout.tie(0);
cin>>lT;
while(lT--){
solve();
}
return 0;
}
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