参考代码:

class Solution:
    def reverseVowels(self, s):
        vowels = set(["a", "e", "i", "o", "u", "A", "E", "I", "O", "U"])
        res = list(s)
        start, end = 0, len(res) = -1
        while start <= end:
            while start <= end and res[start] not in vowels:
                start += 1
            while start <= end and res[end] not in vowels:
                end -= 1
            if start <= end:
                res[start], res[end] = res[end], res[start]
                start += 1
                end -= 1
        return "".join(res)