# 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```
Recommended Practice

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.

Implementation:

## C++

 `// C++ program to reverse order of vowels` `#include` `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

 ``

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.

Implementation:

## C++

 `// C++ program to reverse order of vowels` `#include` `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

 ``

Output

`hollo werld`

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

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