# Remove recurring digits in a given number

• Difficulty Level : Easy
• Last Updated : 23 Jun, 2021

Given a number as string, remove recurring digits from the given string. The changes must be made in-place. Expected time complexity O(n) and auxiliary space O(1).
Examples:

```Input:  num[] = "1299888833"
Output: num[] = "12983"

Input:  num[] = "1299888833222"
Output: num[] = "129832"```

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This problem is similar to Run Length Encoding

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```Let num[] be input number represented as character array

1) Initialize index of modified string 'j' as 0.
2) Traverse input string and do following for every digit num[i].
a) Copy current character 'num[i]' to 'num[j]' and increment i & j.
b) Keep incrementing i while num[i] is same as previous digit.
3) Add string termination character at 'num[j]'```

Below is the implementation of above algorithm.

## C++

 `// C++ program to remove recurring digits from``// a given number``#include ``using` `namespace` `std;` `/* Removes recurring digits in num[]  */``void` `removeRecurringDigits(``char` `num[])``{``    ``int` `len = ``strlen``(num);` `    ``int` `j = 0; ``// Index in modified string` `    ``/* Traverse digits of given number one by one */``    ``for` `(``int` `i=0; i

## Java

 `// Java program to remove recurring``// digits from a given number``class` `GFG``{` `    ``/* Removes recurring digits in num[] */``    ``static` `String removeRecurringDigits(``char` `num[])``    ``{``        ``int` `len = num.length;` `        ``int` `j = ``0``; ``// Index in modified string``        ``String s = ``""``;``        ` `        ``/* Traverse digits of given number one by one */``        ``for` `(``int` `i = ``0``; i < len; i++)``        ``{``            ` `            ``/* Copy the first occurrence of new digit */``            ``s += String.valueOf(num[i]);` `            ``/* Remove repeating occurrences of digit */``            ``while` `(i + ``1` `< len && num[i] == num[i + ``1``])``            ``{``                ``i++;``            ``}``        ``}``        ``return` `s;``    ``}` `    ``/* Driver code */``    ``public` `static` `void` `main(String[] args)``    ``{``        ``char` `num[] = ``"1299888833"``.toCharArray();``        ``System.out.print(``"Modified number is "` `+``                        ``removeRecurringDigits(num));``    ``}``}` `// This code has been contributed by 29AjayKumar`

## Python3

 `# Python3 program to remove recurring``# digits from a given number` `# Removes recurring digits in num[]``def` `removeRecurringDigits(num):` `    ``l ``=` `len``(num)``    ` `    ``# Index in modified string``    ``(i, j) ``=` `(``0``, ``0``)``    ``str` `=` `''``    ` `    ``# Traverse digits of given``    ``# number one by one``    ``while` `i < l:``        ` `        ``# Copy the first occurrence``        ``# of new digit``        ``str` `+``=` `num[i]``        ``j ``+``=` `1``        ` `        ``# Remove repeating occurrences of digit``        ``while` `(i ``+` `1` `< l ``and` `num[i] ``=``=` `num[i ``+` `1``]):``            ``i ``+``=` `1``        ``i ``+``=` `1` `    ``return` `str` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ` `    ``num ``=` `'1299888833'``    ``print``(``'Modified number is {}'``.``format``(``           ``removeRecurringDigits(num)))` `# This code is contributed by rutvik_56`

## C#

 `// C# program to remove recurring``// digits from a given number``using` `System;` `class` `GFG``{` `    ``/* Removes recurring digits in num[] */``    ``static` `String removeRecurringDigits(``char` `[]num)``    ``{``        ``int` `len = num.Length;` `        ``int` `j = 0; ``// Index in modified string``        ``String s = ``""``;``        ` `        ``/* Traverse digits of given number one by one */``        ``for` `(``int` `i = 0; i < len; i++)``        ``{``            ` `            ``/* Copy the first occurrence of new digit */``            ``s += String.Join(``""``,num[i]);` `            ``/* Remove repeating occurrences of digit */``            ``while` `(i + 1 < len && num[i] == num[i + 1])``            ``{``                ``i++;``            ``}``        ``}``        ``return` `s;``    ``}` `    ``/* Driver code */``    ``public` `static` `void` `Main()``    ``{``        ``char` `[]num = ``"1299888833"``.ToCharArray();``        ``Console.Write(``"Modified number is "` `+``                        ``removeRecurringDigits(num));``    ``}``}` `/* This code contributed by PrinciRaj1992 */`

## Javascript

 ``

Output:

`Modified number is 12983`