917. Reverse Only Letters

Given a string s, reverse the string according to the following rules:

• All the characters that are not English letters remain in the same position.
• All the English letters (lowercase or uppercase) should be reversed.

Return s after reversing it.

 

Example 1:

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

Example 2:

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

Example 3:

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

 

Constraints:

• 1 <= s.length <= 100
• s consists of characters with ASCII values in the range [33, 122].
• s does not contain '\"' or '\\'.

---

class Solution(object):
    def reverseOnlyLetters(self, S):
        letters = [c for c in S if c.isalpha()]
        ans = []
        for char in S:
            if char.isalpha():
                ans.append(letters.pop())
            else:
                ans.append(char)
        return "".join(ans)