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".

Solution: Two Pointers

VOWELS = set('aeiouAEIOU')


class Solution(object):
    def reverseVowels(self, s):
        """
        :type s: str
        :rtype: str
        """
        chars = list(s)
        low = 0
        high = len(chars) - 1
        while low < high:
            if chars[low] not in VOWELS:
                low += 1
            elif chars[high] not in VOWELS:
                high -= 1
            else:
                chars[low], chars[high] = chars[high], chars[low]
                low += 1
                high -= 1
        return ''.join(chars)

Lessons:

• Reverse: use two pointers!