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Reverse Vowels of a String

Given a string s, reverse only all the vowels in the string and return it.

The vowels are a, e, i, o, and u, and they can appear in both lower and upper cases, more than once.

My approach:

We know that we’ll be given a string s and our goal is to reverse only all the vowels in the string and return it

If you look at the example it’s more of they swap the vowels where it’s occurring in the left and right side of the string:

Input: s = "hello"
Output: "holle"

So I wrote a script to do the same thing and here’s what it does:

• Store the vowel alphabet in a hashtable
• Initialize two pointers left and right which would hold the 0th and last index len(s)-1
• In a while loop I’ll check the conditions:
  • To check for if the value of s[left] of the string is not a vowel I’ll make a while loop that checks for that and I’ll increment the left pointer by 1
  • To check for if the value of s[right] of the string is not a vowel I’ll make a while loop that checks for that and I’ll decrement the right pointer by 1
  • The point at which they exist two values where s[left] and s[right] is vowel I’ll then swap them i.e set s[left], s[right] = s[right], s[left]
  • Then I’ll increment the left pointer by 1 and decrement the right pointer by 1 to keep the process going till I reach the condition where left > right then the loop finishes

Here’s my solve script: link

Leetcode Submission Script

class Solution:
    def reverseVowels(self, s: str) -> str:
        s = list(s)
        vowels = {"a", "e", "i", "o", "u", "A", "E", "I", "O", "U"}

        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


        r = "".join(s)
        
        return r