917. 仅仅反转字母

class Solution:
    def reverseOnlyLetters(self, s: str) -> str:
        arrs = list(s)
        n = len(s)
        left, right = 0, n-1
        while left< right:
            while left <n and not s[left].isalpha():
                left += 1
            while right>0 and not s[right].isalpha():
                right -= 1
            if left<right:
                arrs[left], arrs[right] = arrs[right], arrs[left]
            left += 1
            right -= 1
        
        return "".join(arrs)