[leetcode] 984. String Without AAA or BBB

Description

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.

分析

题目的意思是：给定a的数量，b的数量，组成一个字符串，要求连续a或者连续b的数量不超过3.

• 我参考了一下答案，直觉的求解释选择当前所剩最多的待写字母写入字符串中。举一个例子，如果 a= 6, b = 2，那么我们期望写出 ‘aabaabaa’
• 用flag标识变量控制当前需要选择的字母就行了，如果flag为True，则选择’a’，否则选择’b’
• 选择’a’的情况是a的长度大于b，或者res结果里面最后连续两个字符是’b’，否则就需要选择’a’

代码

class Solution:
    def strWithout3a3b(self, a: int, b: int) -> str:
        res=''
        flag=False
        while(a>0 or b>0):
            if(len(res)>=2 and res[-1]==res[-2]):
                if(res[-1]=='b'):
                    flag=True
                else:
                    flag=False
            else:
                if(a>b):
                    flag=True
                else:
                    flag=False
            
            if(flag):
                res+='a'
                a-=1
            else:
                res+='b'
                b-=1
        return res

参考文献

不含 AAA 或 BBB 的字符串