# Remove all consecutive duplicates from the string

• Difficulty Level : Easy
• Last Updated : 15 Sep, 2022

Given a string S, The task is to remove all the consecutive duplicate characters of the string and return the resultant string.

Note: that this problem is different from Recursively remove all adjacent duplicates. Here we keep one character and remove all subsequent same characters.

Examples:

Input: S= “aaaaabbbbbb”
Output: ab

Input: S = “geeksforgeeks”
Output: geksforgeks

Input: S = “aabccba”
Output: abcba

## Remove all consecutive duplicates from the string using recursion:

Approach:

If the string is not empty compare the adjacent characters of the string. If they are the same then shift the characters one by one to the left. Call recursion on string S otherwise, call recursion from S+1 string.

Follow the below steps to implement the idea:

• If the string is empty, return.
• Else compare the adjacent characters of the string. If they are the same then shift the characters one by one to the left. Call recursion on string S
• If they are not same then call recursion from S+1 string.

Illustration:

The recursion tree for the string S = aabcca is shown below.

aabcca    S = aabcca
/
abcca            S = abcca
/
bcca                 S = abcca
/
cca                        S = abcca
/
ca                                S = abca
/
a                                     S = abca (Output String)
/
empty string

Below is the implementation of the above approach:

## C++

 `// Recursive Program to remove consecutive` `// duplicates from string S.` `#include ` `using` `namespace` `std;`   `// A recursive function that removes` `// consecutive duplicates from string S` `void` `removeDuplicates(``char``* S)` `{` `    ``// When string is empty, return` `    ``if` `(S == ``'\0'``)` `        ``return``;`   `    ``// if the adjacent characters are same` `    ``if` `(S == S) {`   `        ``// Shift character by one to left` `        ``int` `i = 0;` `        ``while` `(S[i] != ``'\0'``) {` `            ``S[i] = S[i + 1];` `            ``i++;` `        ``}`   `        ``// Check on Updated String S` `        ``removeDuplicates(S);` `    ``}`   `    ``// If the adjacent characters are not same` `    ``// Check from S+1 string address` `    ``removeDuplicates(S + 1);` `}`   `// Driver Program` `int` `main()` `{` `    ``char` `S1[] = ``"geeksforgeeks"``;` `    ``removeDuplicates(S1);` `    ``cout << S1 << endl;`   `    ``char` `S2[] = ``"aabcca"``;` `    ``removeDuplicates(S2);` `    ``cout << S2 << endl;`   `    ``return` `0;` `}`

## Java

 `/*package whatever //do not write package name here */`   `import` `java.io.*;`   `class` `GFG {` `    ``public` `static` `String` `    ``removeConsecutiveDuplicates(String input)` `    ``{` `        ``if` `(input.length() <= ``1``)` `            ``return` `input;` `        ``if` `(input.charAt(``0``) == input.charAt(``1``))` `            ``return` `removeConsecutiveDuplicates(` `                ``input.substring(``1``));` `        ``else` `            ``return` `input.charAt(``0``)` `                ``+ removeConsecutiveDuplicates(` `                       ``input.substring(``1``));` `    ``}` `    ``public` `static` `void` `main(String[] args)` `    ``{` `        ``String S1 = ``"geeksforgeeks"``;` `        ``System.out.println(removeConsecutiveDuplicates(S1));`   `        ``String S2 = ``"aabcca"``;` `        ``System.out.println(removeConsecutiveDuplicates(S2));` `    ``}` `}`

## Python3

 `# Recursive Program to remove consecutive` `# duplicates from string S.`     `def` `removeConsecutiveDuplicates(s):` `    ``if` `len``(s) < ``2``:` `        ``return` `s` `    ``if` `s[``0``] !``=` `s[``1``]:` `        ``return` `s[``0``]``+``removeConsecutiveDuplicates(s[``1``:])` `    ``return` `removeConsecutiveDuplicates(s[``1``:])`     `# This code is contributed by direwolf707` `s1 ``=` `'geeksforgeeks'` `print``(removeConsecutiveDuplicates(s1))  ``# geksforgeks` `s2 ``=` `'aabcca'` `print``(removeConsecutiveDuplicates(s2))  ``# ab`   `# This code is contributed by rahulsood707.`

## C#

 `/*package whatever //do not write package name here */` `using` `System;`   `class` `GFG {` `    ``public` `static` `string` `    ``removeConsecutiveDuplicates(``string` `input)` `    ``{` `        ``if` `(input.Length <= 1)` `            ``return` `input;` `        ``if` `(input == input)` `            ``return` `removeConsecutiveDuplicates(` `                ``input.Substring(1));` `        ``else` `            ``return` `input` `                ``+ removeConsecutiveDuplicates(` `                       ``input.Substring(1));` `    ``}` `    ``public` `static` `void` `Main(String[] args)` `    ``{` `        ``string` `S1 = ``"geeksforgeeks"``;` `        ``Console.WriteLine(removeConsecutiveDuplicates(S1));`   `        ``string` `S2 = ``"aabcca"``;` `        ``Console.Write(removeConsecutiveDuplicates(S2));` `    ``}` `}`   `// This code is contributed by shivanisinghss2110`

## Javascript

 ``

Output

```geksforgeks
abca
```

Time complexity: O(N2)
Auxiliary Space: O(1)

## Remove all consecutive duplicates from the string using Iterative approach:

The idea is to check if current character is equal to the next character or not . If current character is equal to the next character we’ll ignore it and when it is not equal we will add it to our answer. At last add the last character.

Follow the below steps to implement the idea:

• Create an str string to store the result
• Iterate form 0 to string length – 2.
• If the current character is not equal to next character then add it to answer string.
• Else continue.
• return str.

Below is the implementation of above approach:

## C++

 `// C++ program to remove consecutive` `// duplicates from a given string.` `#include ` `using` `namespace` `std;`   `// A iterative function that removes` `// consecutive duplicates from string S` `string removeDuplicates(string s)` `{`   `    ``int` `n = s.length();` `    ``string str = ``""``;` `    ``// We don't need to do anything for` `    ``// empty string.` `    ``if` `(n == 0)` `        ``return` `str;`   `    ``// Traversing string` `    ``for` `(``int` `i = 0; i < n - 1; i++) {` `        ``// checking if s[i] is not same as s[i+1] then add` `        ``// it into str` `        ``if` `(s[i] != s[i + 1]) {` `            ``str += s[i];` `        ``}` `    ``}` `    ``// Since the last character will not be inserted in the` `    ``// loop we add it at the end` `    ``str.push_back(s[n - 1]);` `    ``return` `str;` `}`   `// Driver Program` `int` `main()` `{`   `    ``string s1 = ``"geeksforgeeks"``;` `    ``cout << removeDuplicates(s1) << endl;`   `    ``string s2 = ``"aabcca"``;` `    ``cout << removeDuplicates(s2) << endl;`   `    ``return` `0;` `}`

## Java

 `// Java program to remove consecutive` `// duplicates from a given string.` `import` `java.util.*;`   `class` `GFG {`   `    ``// A iterative function that removes` `    ``// consecutive duplicates from string S` `    ``static` `void` `removeDuplicates(``char``[] S)` `    ``{` `        ``int` `n = S.length;`   `        ``// We don't need to do anything for` `        ``// empty or single character string.` `        ``if` `(n < ``2``) {` `            ``return``;` `        ``}`   `        ``// j is used to store index is result` `        ``// string (or index of current distinct` `        ``// character)` `        ``int` `j = ``0``;`   `        ``// Traversing string` `        ``for` `(``int` `i = ``1``; i < n; i++) {` `            ``// If current character S[i]` `            ``// is different from S[j]` `            ``if` `(S[j] != S[i]) {` `                ``j++;` `                ``S[j] = S[i];` `            ``}` `        ``}` `        ``System.out.println(Arrays.copyOfRange(S, ``0``, j + ``1``));` `    ``}`   `    ``// Driver code` `    ``public` `static` `void` `main(String[] args)` `    ``{` `        ``char` `S1[] = ``"geeksforgeeks"``.toCharArray();` `        ``removeDuplicates(S1);`   `        ``char` `S2[] = ``"aabcca"``.toCharArray();` `        ``removeDuplicates(S2);` `    ``}` `}`   `/* This code contributed by PrinciRaj1992 */`

## Python3

 `# Python3 program to remove consecutive` `# duplicates from a given string.`   `# A iterative function that removes` `# consecutive duplicates from string S`     `def` `removeDuplicates(S):`   `    ``n ``=` `len``(S)`   `    ``# We don't need to do anything for` `    ``# empty or single character string.` `    ``if` `(n < ``2``):` `        ``return`   `    ``# j is used to store index is result` `    ``# string (or index of current distinct` `    ``# character)` `    ``j ``=` `0`   `    ``# Traversing string` `    ``for` `i ``in` `range``(n):`   `        ``# If current character S[i]` `        ``# is different from S[j]` `        ``if` `(S[j] !``=` `S[i]):` `            ``j ``+``=` `1` `            ``S[j] ``=` `S[i]`   `    ``# Putting string termination` `    ``# character.` `    ``j ``+``=` `1` `    ``S ``=` `S[:j]` `    ``return` `S`     `# Driver Code` `if` `__name__ ``=``=` `'__main__'``:`   `    ``S1 ``=` `"geeksforgeeks"` `    ``S1 ``=` `list``(S1.rstrip())` `    ``S1 ``=` `removeDuplicates(S1)` `    ``print``(``*``S1, sep``=``"")`   `    ``S2 ``=` `"aabcca"` `    ``S2 ``=` `list``(S2.rstrip())` `    ``S2 ``=` `removeDuplicates(S2)` `    ``print``(``*``S2, sep``=``"")`   `# This code is contributed by` `# Shubham Singh(SHUBHAMSINGH10)`

## C#

 `// C# program to remove consecutive` `// duplicates from a given string.` `using` `System;`   `class` `GFG {`   `    ``// A iterative function that removes` `    ``// consecutive duplicates from string S` `    ``static` `void` `removeDuplicates(``char``[] S)` `    ``{` `        ``int` `n = S.Length;`   `        ``// We don't need to do anything for` `        ``// empty or single character string.` `        ``if` `(n < 2) {` `            ``return``;` `        ``}`   `        ``// j is used to store index is result` `        ``// string (or index of current distinct` `        ``// character)` `        ``int` `j = 0;`   `        ``// Traversing string` `        ``for` `(``int` `i = 1; i < n; i++) {` `            ``// If current character S[i]` `            ``// is different from S[j]` `            ``if` `(S[j] != S[i]) {` `                ``j++;` `                ``S[j] = S[i];` `            ``}` `        ``}` `        ``char``[] A = ``new` `char``[j + 1];` `        ``Array.Copy(S, 0, A, 0, j + 1);` `        ``Console.WriteLine(A);` `    ``}`   `    ``// Driver code` `    ``public` `static` `void` `Main(String[] args)` `    ``{` `        ``char``[] S1 = ``"geeksforgeeks"``.ToCharArray();` `        ``removeDuplicates(S1);`   `        ``char``[] S2 = ``"aabcca"``.ToCharArray();` `        ``removeDuplicates(S2);` `    ``}` `}`   `// This code is contributed by 29AjayKumar`

## Javascript

 ``

Output

```geksforgeks
abca
```

Time Complexity: O(N)
Auxiliary Space: O(1)

This article is contributed by Ankur Singh. 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.

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