Description
Given a string s consisting only of letters ‘a’ and ‘b’. In a single step you can remove one palindromic subsequence from s.
Return the minimum number of steps to make the given string empty.
A string is a subsequence of a given string, if it is generated by deleting some characters of a given string without changing its order.
A string is called palindrome if is one that reads the same backward as well as forward.
Example 1:
Input: s = "ababa"
Output: 1
Explanation: String is already palindrome
Example 2:
Input: s = "abb"
Output: 2
Explanation: "abb" -> "bb" -> "".
Remove palindromic subsequence "a" then "bb".
Example 3:
Input: s = "baabb"
Output: 2
Explanation: "baabb" -> "b" -> "".
Remove palindromic subsequence "baab" then "b".
Example 4:
Input: s = ""
Output: 0
Constraints:
- 0 <= s.length <= 1000
- s only consists of letters ‘a’ and ‘b’
分析
题目的意思是：移除字符串的回文子串，直至为空串。这里有个规律，就是回文子串只由a，b组成，所以最多2次就能把原来的字符串变为空串，所以如果s字符串本身为空串的话，返回0；如果s本身就是回文子串的话，则返回1；否则返回2.如果发现这个规律，代码就比较简单了。
代码
class Solution:
def removePalindromeSub(self, s: str) -> int:
return 2-(s==s[::-1])-(s=='')
参考文献
[LeetCode] [Java/C++/Python] Maximum 2 Operations