Company: Visa_6nov
Difficulty: medium
Concatenated Digit Sums Problem Description You are given two numerical strings, and your task is to return a string of their digits, as described below. Add every i-th digit of the first string to the i-th digit of the second string, both counted from the end. If the i-th digit of one of the strings is absent, the sum will be the i-th digit of the other string. Return a string of those sums concatenated with each other. Note: You are not expected to provide the most optimal solution, but a solution with time complexity not worse than O(max(a.length, b.length)^2) will fit within the execution time limit. Examples Example 1: Input: a = "99", b = "99" Output: "1818" Explanation: Counting from the end: For the 1st digit from the end: 9 (from 'a') + 9 (from 'b') = 18. For the 2nd digit from the end: 9 (from 'a') + 9 (from 'b') = 18. Concatenating these sums in order from left to right (corresponding to processing from the beginning of the string to the end, or prepending sums processed fro