Reverse Vowels of a String

String Simulation

Problem

Write a function that takes a string as input and reverse only the vowels of a string.

For example:

Input: "hello"
Output: "holle"

Input: "leetcode"
Output: "leotcede"

Thought Process

• You can use 2 pointer approach for this problem

• We have to convert the string to a list in order to reassign elements

Solution

class Solution:
    def reverseVowels(self, s: str) -> str:
        
        s = list(s) 
    # converting string to list 
    # because strings do not support 
    # item assignment 
        vowels = 'aeiouAEIOU'
        i = 0
        j = len(s)-1
        
        while i < j:
            while i < j and s[i] not in vowels: #finding the first vowel we come across
                i+=1
            while i < j and s[j] not in vowels: #finding the first vowel we come across
                j-=1
            
            s[i], s[j] = s[j], s[i]
            i+=1
            j-=1
        return "".join(s)
            

Time Complexity

• Time: O(n) since we are using the two pointer approach and going linearly. Also, when we look up to see if the element is a vowel, it will take O(10) which is just O(1)

• Space: O(1)