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345. Reverse Vowels of a String

Basant Babu Bhandari's photo
Basant Babu Bhandari
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1 min read

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.

Example 1:

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

Example 2:

Input: s = "leetcode"
Output: "leotcede"

Constraints:

  • 1 <= s.length <= 3 * 10<sup>5</sup>

  • s consist of printable ASCII characters.

Solution:

class Solution:
    def reverseVowels(self, s: str) -> str:
        """
        solved using two pointer problem
        """
        s=list(s)
        left=0
        right=len(s)-1

        vowels=set('AEIOUaeiou')
        # loop until left pointer is less then right pointer
        while left<right:
            # shift left pointer toward right until it finds the vowel
            while left<right and s[left] not in vowels:
                left+=1
            # shift right pointer toward left until it finds the vowel
            while left<right and s[right] not in vowels:
                right-=1
            # interchange the vowel char
            s[left],s[right]=s[right],s[left]
            # update left and right pointer
            left+=1
            right-=1

        return ''.join(s)
DSA