编写一个函数，以字符串作为输入，反转该字符串中的元音字母。
示例 1:
输入: "hello"
输出: "holle"
示例 2:
输入: "leetcode"
输出: "leotcede"说明:
元音字母不包含字母"y"。
class Solution:
def reverseVowels(self, s):
"""
:type s: str
:rtype: str
"""
start = 0
end = len(s)-1
if end <= start:
return s
tmp = list(s)
limit = 'aeiouAEIOU'
while start < end:
if tmp[start] not in limit:
start += 1
elif tmp[end] not in limit:
end -= 1
else:
tmp[start],tmp[end]=tmp[end],tmp[start]
start += 1
end -= 1
return ''.join(tmp)
