## AND Sorting solution codeforces

You are given a permutation pp of integers from 00 to n−1n−1 (each of them occurs exactly once). Initially, the permutation is not sorted (that is, pi>pi+1pi>pi+1 for at least one 1≤i≤n−11≤i≤n−1).

The permutation is called XX-sortable for some non-negative integer XX if it is possible to sort the permutation by performing the operation below some finite number of times:

- Choose two indices ii and jj (1≤i<j≤n)(1≤i
such that pi&pj=Xpi&pj=X. - Swap pipi and pjpj.

Here && denotes the bitwise AND operation.

Find the maximum value of XX such that pp is XX-sortable. It can be shown that there always exists some value of XX such that pp is XX-sortable.

The input consists of multiple test cases. The first line contains a single integer tt (1≤t≤104)(1≤t≤104) — the number of test cases. Description of test cases follows.

The first line of each test case contains a single integer nn (2≤n≤2⋅105)(2≤n≤2⋅105) — the length of the permutation.

The second line of each test case contains nn integers p1,p2,...,pnp1,p2,…,pn (0≤pi≤n−10≤pi≤n−1, all pipi are distinct) — the elements of pp. It is guaranteed that pp is not sorted.

It is guaranteed that the sum of nn over all cases does not exceed 2⋅1052⋅105.

For each test case output a single integer — the maximum value of XX such that pp is XX-sortable.

4 4 0 1 3 2 2 1 0 7 0 1 2 3 5 6 4 5 0 3 2 1 4

2 0 4 1

In the first test case, the only XX for which the permutation is XX-sortable are X=0X=0 and X=2X=2, maximum of which is 22.

Sorting using X=0X=0:

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- Swap p1p1 and p4p4, p=[2,1,3,0]p=[2,1,3,0].
- Swap p3p3 and p4p4, p=[2,1,0,3]p=[2,1,0,3].
- Swap p1p1 and p3p3, p=[0,1,2,3]p=[0,1,2,3].

Sorting using X=2X=2:

- Swap p3p3 and p4p4, p=[0,1,2,3]p=[0,1,2,3].

In the second test case, we must swap p1p1 and p2p2 which is possible only with X=0X=0.

## SOLUTION

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