# 345 Reverse Vowels of a String

Write a function that takes a string as input and reverse only the vowels of a string.
Example 1: Given s = "hello", return "holle".
Example 2: Given s = "leetcode", return "leotcede".
Note: The vowels does not include the letter "y".
The Idea:
• Swap the first and back occurances respectively.
string reverseVowels(string s) {
unordered_set<char> vowels = { 'a', 'e', 'i', 'o', 'u',
'A', 'E', 'I', 'O', 'U'};
int iter_front = 0;
int iter_back = s.size() - 1;
while (iter_front < iter_back) {
while (iter_front < iter_back && vowels.find(s[iter_front]) == vowels.end())
iter_front++;
while (iter_front < iter_back && vowels.find(s[iter_back]) == vowels.end())
iter_back--;
swap(s[iter_front], s[iter_back]);
iter_front++;
iter_back--;
}
return s;
}
int main() {
string s = "hello";
cout << reverseVowels(s) << endl;
return 0;
}
Python
class Solution(object):
def reverseVowels(self, s):
"""
:type s: str
:rtype: str
"""
vowels = {'a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'}
s = list(s)
left, right = 0, len(s) - 1
while left < right:
while left < right and s[left] not in vowels:
left += 1
while left < right and s[right] not in vowels:
right -= 1
if s[left] in vowels and s[right] in vowels:
s[left], s[right] = s[right], s[left]
left += 1
right -= 1
else:
break
return ''.join(s)