984. String Without AAA or BBB

Problem

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.

Solution (Java)

class Solution {
    public String strWithout3a3b(int a, int b) {
        String first = a > b ? "a" : "b";
        String second = first.equals("a") ? "b" : "a";
        int firstLen = Math.max(a, b);
        int secondLen = Math.min(a, b);
        StringBuilder ans = new StringBuilder();
        // Case 1 : A and B count are unequal.
        while (firstLen > 0 && secondLen > 0 && firstLen != secondLen) {
            ans.append(first);
            ans.append(first);
            firstLen = firstLen - 2;
            ans.append(second);
            secondLen--;
        }
        // Case 2: A and B count are equal
        while (firstLen > 0 && secondLen > 0) {
            ans.append(first);
            ans.append(second);
            firstLen--;
            secondLen--;
        }
        // left over, just append
        while (firstLen > 0) {
            ans.append(first);
            firstLen--;
        }
        return ans.toString();
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).