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

/**
 * @param {number} a
 * @param {number} b
 * @return {string}
 */
var strWithout3a3b = function(a, b, isRevert) {
    if (b > a) return strWithout3a3b(b, a, true);
    var res = '';
    while (a > 0 || b > 0) {
        if (a > 0) {
            var num = a > 2 ? 2 : 1;
            res += (isRevert ? 'b' : 'a').repeat(num);
            a -= num;
        }
        if (b > 0) {
            var num = b > Math.ceil(a / 2) && b >= 2 ? 2 : 1;
            res += (isRevert ? 'a' : 'b').repeat(num);
            b -= num;
        }
    }
    return res;
};

Explain:

nope.

Complexity:

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