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; 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"
Note:
- 0 <= A <= 100
- 0 <= B <= 100
- It is guaranteed such an S exists for the given A and B.