Reverse Vowels of a String

Description

Reverse Vowels of a String - LeetCode

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.

Examples

Example 1:

Input: s = “IceCreAm” Output: “AceCreIm” Explanation: The vowels in s are ['I', 'e', 'e', 'A']. On reversing the vowels, s becomes "AceCreIm".

Example 2:

Input: s = “leetcode” Output: “leotcede”

Constraint

• $1<=\text{s.length}<=3\ast 10^5$
• s consist of printable ASCII characters.

Code

class Solution {
public:
    string reverseVowels(string s) {
        string word = s;
        int front = 0;
        int back = s.length() - 1;
        const string vowels = "aeiouAEIOU";
  
        while(front < back){
            bool frontOK = vowels.find(word[front]) != string::npos;
            bool backOK = vowels.find(word[back]) != string::npos;
            if (frontOK && backOK) {
                swap(word[front], word[back]);
                front++;
                back--;
            }
            if (!frontOK) front++;
            if (!backOK) back--;
        }
  
        return word;
    }
};

Approach

1. Create result word, front, back, and vowels variables
2. Loop through with 2 pointers until there the front is ahead of the back
   1. Check if both front and back are both vowels
      • Swap the front and back
      • Update front and back
   2. Check if front is a vowel
      • Update front
   3. Check if back is a vowel
      • Update back
3. Return the result word