[LeetCode&Python] Problem 917. Reverse Only Letters

Given a string S, return the "reversed" string where all characters that are not a letter stay in the same place, and all letters reverse their positions.

 

 

Example 1:

Input: "ab-cd"
Output: "dc-ba"

Example 2:

Input: "a-bC-dEf-ghIj"
Output: "j-Ih-gfE-dCba"

Example 3:

Input: "Test1ng-Leet=code-Q!"
Output: "Qedo1ct-eeLg=ntse-T!"

 

Note:

1. S.length <= 100
2. 33 <= S[i].ASCIIcode <= 122 
3. S doesn't contain \ or "

class Solution:
    def reverseOnlyLetters(self, S):
        """
        :type S: str
        :rtype: str
        """
        
        n=len(S)
        s=list(S)
        i=0
        j=n-1
        while i<j:
            while i<j and not s[i].isalpha():i+=1
            while i<j and not s[j].isalpha():j-=1
            s[i],s[j]=s[j],s[i]
            i+=1
            j-=1
        return ''.join(s)