# 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: Please solve it on “PRACTICE” first, before moving on to the solution.

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 ` `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 ` `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)

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