Reverse vowels in a given string

Given a string, your task is to reverse only the vowels of string.

Examples:

Input : hello
Output : holle

Input : hello world
Output : hollo werld

One simple solution is to store all the vowels while scanning the string and placing the vowels in the reverse order in another iteration of string.

C++



filter_none

edit
close

play_arrow

link
brightness_4
code

// C++ program to reverse order of vowels
#include<bits/stdc++.h>
using namespace std;
  
// utility function to check for vowel
bool isVowel(char c)
{
    return (c=='a' || c=='A' || c=='e' ||
            c=='E' || c=='i' || c=='I' ||
            c=='o' || c=='O' || c=='u' ||
            c=='U');
}
  
// Function to reverse order of vowels
string reverseVowel(string str)
{
    int j=0;
    // Storing the vowels separately
    string vowel;
    for (int i=0; str[i]!='\0'; i++)
        if (isVowel(str[i]))
            vowel[j++] = str[i];
  
    // Placing the vowels in the reverse
    // order in the string
    for (int i=0; str[i]!='\0'; i++)
        if (isVowel(str[i]))
            str[i] = vowel[--j] ;
  
    return str;
}
  
// Driver function
int main()
{
    string str = "hello world";
    cout << reverseVowel(str);
    return 0;
}

chevron_right


Java

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java program to reverse order of vowels
  
class GFG {
  
// utility function to check for vowel
    static boolean isVowel(char c) {
        return (c == 'a' || c == 'A' || c == 'e'
                || c == 'E' || c == 'i' || c == 'I'
                || c == 'o' || c == 'O' || c == 'u'
                || c == 'U');
    }
  
// Function to reverse order of vowels
    static String reverseVowel(String str1) {
        int j = 0;
        // Storing the vowels separately
        char[] str = str1.toCharArray();
        String vowel = "";
        for (int i = 0; i < str.length; i++) {
            if (isVowel(str[i])) {
                j++;
                vowel += str[i];
            }
        }
  
        // Placing the vowels in the reverse
        // order in the string
        for (int i = 0; i < str.length; i++) {
            if (isVowel(str[i])) {
                str[i] = vowel.charAt(--j);
            }
        }
  
        return String.valueOf(str);
    }
  
// Driver function
    public static void main(String[] args) {
        String str = "hello world";
        System.out.println(reverseVowel(str));
    }
  
// This code is contributed by princiRaj1992

chevron_right


C#

filter_none

edit
close

play_arrow

link
brightness_4
code

// C# program to reverse order of vowels
using System;
  
class GFG
{
  
    // utility function to check for vowel
    static bool isVowel(char c) 
    {
        return (c == 'a' || c == 'A' || c == 'e'
                || c == 'E' || c == 'i' || c == 'I'
                || c == 'o' || c == 'O' || c == 'u'
                || c == 'U');
    }
  
    // Function to reverse order of vowels
    static String reverseVowel(String str1)
    {
        int j = 0;
          
        // Storing the vowels separately
        char[] str = str1.ToCharArray();
        String vowel = "";
        for (int i = 0; i < str.Length; i++)
        {
            if (isVowel(str[i]))
            {
                j++;
                vowel += str[i];
            }
        }
  
        // Placing the vowels in the reverse
        // order in the string
        for (int i = 0; i < str.Length; i++)
        {
            if (isVowel(str[i]))
            {
                str[i] = vowel[--j];
            }
        }
  
        return String.Join("",str);
    }
  
    // Driver code
    public static void Main(String[] args)
    {
        String str = "hello world";
        Console.WriteLine(reverseVowel(str));
    }
}
  
// This code has been contributed by 29AjayKumar

chevron_right


Output:

hollo werld

Time complexity : O(n) where n = length of string
Auxiliary Space : O(v) where v = number of vowels in string

A better solution is to use two pointers scanning from beginning and end of the array respectively and manipulate vowels pointed by these pointers.

C++

filter_none

edit
close

play_arrow

link
brightness_4
code

// C++ program to reverse order of vowels
#include<bits/stdc++.h>
using namespace std;
  
// utility function to check for vowel
bool isVowel(char c)
{
    return (c=='a' || c=='A' || c=='e' ||
            c=='E' || c=='i' || c=='I' ||
            c=='o' || c=='O' || c=='u' ||
            c=='U');
}
  
// Function to reverse order of vowels
string reverseVowel(string str)
{
    // Start two indexes from two corners
    // and move toward each other
    int i = 0;
    int j = str.length()-1;
    while (i < j)
    {
        if (!isVowel(str[i]))
        {
            i++;
            continue;
        }
        if (!isVowel(str[j]))
        {
            j--;
            continue;
        }
  
        // swapping
        swap(str[i], str[j]);
  
        i++;
        j--;
    }
  
    return str;
}
  
// Driver function
int main()
{
    string str = "hello world";
    cout << reverseVowel(str);
    return 0;
}

chevron_right


Java

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java program to reverse order of vowels
  
class GFG {
  
// utility function to check for vowel
    static boolean isVowel(char c) {
        return (c == 'a' || c == 'A' || c == 'e'
                || c == 'E' || c == 'i' || c == 'I'
                || c == 'o' || c == 'O' || c == 'u'
                || c == 'U');
    }
  
// Function to reverse order of vowels
static String reverseVowel(String str) {
    // Start two indexes from two corners
    // and move toward each other
    int i = 0;
    int j = str.length()-1;
    char[] str1 = str.toCharArray();
    while (i < j)
    {
        if (!isVowel(str1[i]))
        {
            i++;
            continue;
        }
        if (!isVowel(str1[j]))
        {
            j--;
            continue;
        }
  
        // swapping
        char t = str1[i];
        str1[i]= str1[j];
        str1[j]= t;
          
  
        i++;
        j--;
    }
    String str2 = String.copyValueOf(str1);
    return str2;
}
  
// Driver function
    public static void main(String[] args) {
        String str = "hello world";
        System.out.println(reverseVowel(str));
    }
}

chevron_right



Output:

hollo werld

Time complexity : O(n) where n = length of string
Auxiliary Space : O(1)

This article is contributed by Gaurav Ahirwar and Gaurav Miglani. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.



My Personal Notes arrow_drop_up



Article Tags :
Practice Tags :


1


Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.