Special Sum of Array Problem Statement

Given an array 'arr' containing single-digit integers, your task is to calculate the total sum of all its elements. However, the resulting sum must also be a single-digit number. To achieve this, repeatedly sum the digits of the result until a single-digit number is obtained.

Example:

Input:

[5, 8, 4, 9]

Output:

8

Explanation:

The sum of the elements is 26. The sum of the digits 2 + 6 = 8 is a single-digit number.

Constraints:

• 1 <= T <= 100
• 1 <= N <= 10^3
• 0 <= arr[i] <= 9
• The sum of 'N' across all test cases does not exceed 10^5.

Time Limit: 1 sec.