Given two integers a and b, return any string s such that: s has length a + b and contains exactly a 'a' letters, and exactly b 'b' letters, The substring 'aaa' does not occur in s, and The substring 'bbb' does not occur in s. Example 1: Input: a = 1, b = 2 Output: "abb" Explanation: "abb", "bab" and "bba" are all correct answers. Example 2: Input: a = 4, b = 1 Output: "aabaa" Constraints: 0 <= a, b <= 100 It is guaranteed such an s exists for the given a and b.