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
        """
        temp = []
        for i in S:
            if i.isalpha():
                temp.append(i)
        res = ''
        for i in S:
            if i.isalpha():
                res += temp.pop()
            else:
                res += i
        return res