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 '\\'.

SOLUTION:

class Solution:
    def reverseOnlyLetters(self, s: str) -> str:
        s = list(s)
        n = len(s)
        stack = []
        for i in range(n):
            if s[i].islower() or s[i].isupper():
                stack.append(s[i])
                s[i] = -1
        for i in range(n):
            if s[i] == -1:
                s[i] = stack.pop()
        return "".join(s)