Half of Same

1000ms

262144K

Description:

This problem is a complicated version of D1, but it has significant differences, so read the whole statement.

Polycarp has an array of $$$n$$$ ($$$n$$$ is even) integers $$$a_1, a_2, \dots, a_n$$$. Polycarp conceived of a positive integer $$$k$$$. After that, Polycarp began performing the following operations on the array: take an index $$$i$$$ ($$$1 \le i \le n$$$) and reduce the number $$$a_i$$$ by $$$k$$$.

After Polycarp performed some (possibly zero) number of such operations, it turned out that at least half of the numbers in the array became the same. Find the maximum $$$k$$$ at which such a situation is possible, or print $$$-1$$$ if such a number can be arbitrarily large.

Input:

The first line contains one integer $$$t$$$ ($$$1 \le t \le 10$$$) — the number of test cases. Then $$$t$$$ test cases follow.

Each test case consists of two lines. The first line contains an even integer $$$n$$$ ($$$4 \le n \le 40$$$) ($$$n$$$ is even). The second line contains $$$n$$$ integers $$$a_1, a_2, \dots a_n$$$ ($$$-10^6 \le a_i \le 10^6$$$).

It is guaranteed that the sum of all $$$n$$$ specified in the given test cases does not exceed $$$100$$$.

Output:

For each test case output on a separate line an integer $$$k$$$ ($$$k \ge 1$$$) — the maximum possible number that Polycarp used in operations on the array, or $$$-1$$$, if such a number can be arbitrarily large.

Sample Input:

4
6
48 13 22 -15 16 35
8
-1 0 1 -1 0 1 -1 0
4
100 -1000 -1000 -1000
4
1 1 1 1

Sample Output:

Informação

Provedor Codeforces

Código CF1593D2