B'You are given an unsorted permutation p_1, p_2, ldots, p_n . To sort the permutation, you choose a constant k ( k ge 1 ) and do some operations on the permutation. In one operation, you can choose two integers i , j ( 1 <= j < i <= n ) such that i - j = k , then swap p_i and p_j . What is the maximum value of k that you can choose to sort the given permutation? A permutation is an array consisting of n distinct integers from 1 to n in arbitrary order. For example, [2, 3, 1, 5, 4] is a permutation, but [1, 2, 2] is not a permutation ( 2 appears twice in the array) and [1, 3, 4] is also not a permutation ( n = 3 but there is 4 in the array). An unsorted permutation p is a permutation such that there is at least one position i that satisfies p_i ne i . Each test contains multiple test cases. The first line contains the number of test cases t ( 1 <= t <= 10^4 ). The description of the test cases follows. The first line of each test case contains a single integer n ( 2 <= n <= 10^{5} ) -- the length of the permutation p . The second line of each test case contains n distinct integers p_1, p_2, ldots, p_n ( 1 <= p_i <= n ) -- the permutation p . It is guaranteed that the given numbers form a permutation of length n and the given permutation is unsorted. It is guaranteed that the sum of n over all test cases does not exceed 2 cdot 10^{5} . For each test case, output the maximum value of k that you can choose to sort the given permutation. We can show that an answer always exists. In the first test case, the maximum value of k you can choose is 1 . The operations used to sort the permutation are: In the second test case, the maximum value of k you can choose is 2 . The operations used to sort the permutation are: '...