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Reverse vowels in a given string
  • Difficulty Level : Easy
  • Last Updated : 10 Feb, 2020

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++




// 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;
}


Java




// 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


Python3




# Python3 program to reverse order of vowels
  
# utility function to check for vowel
def isVowel(c):
    if (c == 'a' or c == 'A' or c == 'e' or 
        c == 'E' or c == 'i' or c == 'I' or 
        c == 'o' or c == 'O' or c == 'u' or c == 'U'):
        return True
    return False
  
# Function to reverse order of vowels
def reverserVowel(string):
    j = 0
    vowel = [0] * len(string)
    string = list(string)
  
    # Storing the vowels separately
    for i in range(len(string)):
        if isVowel(string[i]):
            vowel[j] = string[i]
            j += 1
  
    # Placing the vowels in the reverse
    # order in the string
    for i in range(len(string)):
        if isVowel(string[i]):
            j -= 1
            string[i] = vowel[j]
  
    return ''.join(string)
  
# Driver Code
if __name__ == "__main__":
    string = "hello world"
    print(reverserVowel(string))
  
# This code is contributed by
# sanjeev2552


C#




// 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


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++




// 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;
}


Java




// 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));
    }
}


Python3




# Python3 program to reverse order of vowels 
  
# utility function to check for vowel 
def isVowel(c):
    return (c=='a' or c=='A' or c=='e' or
            c=='E' or c=='i' or c=='I' or
            c=='o' or c=='O' or c=='u' or
            c=='U'
  
# Function to reverse order of vowels 
def reverseVowel(str):
  
    # Start two indexes from two corners 
    # and move toward each other 
    i = 0
    j = len(str) - 1
    while (i < j):
        if not isVowel(str[i]):
            i += 1
            continue
        if (not isVowel(str[j])):
            j -= 1
            continue
          
        # swapping 
        str[i], str[j] = str[j], str[i]
        i += 1
        j -= 1
    return str
  
# Driver function 
if __name__ == "__main__":
    str = "hello world"
    print(*reverseVowel(list(str)), sep = "")
  
# This code is contributed by SHUBHAMSINGH10


C#




// C# program to reverse order of vowels 
using System; 
  
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.Join("",str1); 
    return str2; 
  
// Driver code
public static void Main(String[] args) 
    String str = "hello world"
    Console.WriteLine(reverseVowel(str)); 
  
// This code is contributed by Rajput-Ji



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.

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