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Reverse vowels in a given string

  • Difficulty Level : Easy
  • Last Updated : 29 Jun, 2021

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

Input : hello
Output : holle

Input : hello world
Output : hollo werld

 

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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

Javascript




<script>
 
    // JavaScript program to reverse order of vowels
     
    // utility function to check for vowel
    function isVowel(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
    function reverseVowel(str1) {
        let j = 0;
        // Storing the vowels separately
        let str = str1.split('');
        let vowel = "";
        for (let 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 (let i = 0; i < str.length; i++) {
            if (isVowel(str[i])) {
                str[i] = vowel[--j];
            }
        }
   
        return str.join("");
    }
     
    let str = "hello world";
      document.write(reverseVowel(str));
         
</script>

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

Javascript




<script>
 
// JavaScript program to reverse order of vowels
 
// utility function to check for vowel
function isVowel(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
function reverseVowel(str)
{
    // Start two indexes from two corners
    // and move toward each other
    let i = 0;
    let j = str.length-1;
    let str1 = str.split("");
    while (i < j)
    {
        if (!isVowel(str1[i]))
        {
            i++;
            continue;
        }
        if (!isVowel(str1[j]))
        {
            j--;
            continue;
        }
  
        // swapping
        let t = str1[i];
        str1[i]= str1[j];
        str1[j]= t;
          
  
        i++;
        j--;
    }
    let str2 = (str1).join("");
    return str2;
}
 
// Driver function
let str = "hello world";
document.write(reverseVowel(str));
 
 
 
// This code is contributed by rag2127
 
</script>

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 write.geeksforgeeks.org or mail your article to review-team@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.
 




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