【leetcode】1328. Break a Palindrome

题目如下：

Given a palindromic string palindrome, replace exactly one character by any lowercase English letter so that the string becomes the lexicographically smallest possible string that isn't a palindrome.

After doing so, return the final string.  If there is no way to do so, return the empty string.

Example 1:

Input: palindrome = "abccba"
Output: "aaccba"

Example 2:

Input: palindrome = "a"
Output: ""

Constraints:

• 1 <= palindrome.length <= 1000
• palindrome consists of only lowercase English letters.

解题思路：从左向右遍历palindrome，把第一个不是a的字符转换成a即可，并且要满足转换后的字符串不是回文字符串。

代码如下：

class Solution(object):
    def breakPalindrome(self, palindrome):
        """
        :type palindrome: str
        :rtype: str
        """
        for i in range(len(palindrome)):
            if palindrome[i] == 'a':
                continue
            v = palindrome[:i] + 'a' + palindrome[i+1:]
            if v == v[::-1]:continue
            return palindrome[:i] + 'a' + palindrome[i+1:]
        if len(palindrome) == 1:
            return ''
        elif palindrome[-1] == 'a':
            return palindrome[:-1] + 'b'
        return palindrome[:-1] + 'a'