String Without AAA or BBB — LeetCode 984 Python Solution

The 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

Input

a = 1, b = 2

Output

"abb"

Explanation

"abb", "bab" and "bba" are all correct answers.

Python solution

class Solution:
    def strWithout3a3b(self, a: int, b: int) -> str:
        ans = []
        while a and b:
            if a > b:
                ans.append('aab')
                a, b = a - 2, b - 1
            elif a < b:
                ans.append('bba')
                a, b = a - 1, b - 2
            else:
                ans.append('ab')
                a, b = a - 1, b - 1
        if a:
            ans.append('a' * a)
        if b:
            ans.append('b' * b)
        return ''.join(ans)

Complexity

Pattern: Greedy

Take the locally best option every time — when you can prove that never costs you later. LeetCode 984. String Without AAA or BBB is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Greedy.

The greedy guide has the Python template for the pattern and the 346 LeetCode problems that use it.

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