Remove first adjacent pairs of similar characters until possible

Given a string Str, the task is to remove first adjacent pairs of similar characters until we can. 
Note: Remove adjacent characters to get a new string and then again remove adjacent duplicates from the new string and keep repeating this process until all similar adjacent character pairs are removed.
Examples:

Input: str = “keexxllx” 
Output: kx 
Step 0: Remove ee to get “kxxllx” 
Step 1: Remove xx to get “kllx” 
Step 2: Remove ll to get “kx” 
Input: str = “abbaca” 
Output: ca 

Approach: 
Use string’s back() and pop_back() method STL in C++ to solve the above problem. Iterate for every character in the string, and if the adjacent characters are same, then remove the adjacent characters using pop_back() function. At the end, return the final string. 
Below is the implementation of the above approach: 

C++

// C++ implementation of the above approach
#include <bits/stdc++.h>
using namespace std;

// Function to remove adjacent duplicates
string removeDuplicates(string S)
{
    string ans = "";

    // Iterate for every character
    // in the string
    for (auto it : S) {

        // If ans string is empty or its last
        // character does not match with the
        // current character then append this
        // character to the string
        if (ans.empty() or ans.back() != it)
            ans.push_back(it);

        // Matches with the previous one
        else if (ans.back() == it)
            ans.pop_back();
    }

    // Return the answer
    return ans;
}

// Driver Code
int main()
{
    string str = "keexxllx";
    cout << removeDuplicates(str);
}

Java

// Java implementation of the above approach
class GFG
{

    // Function to remove adjacent duplicates
    static String removeDuplicates(String S)
    {
        String ans = "";

        // Iterate for every character
        // in the string
        for (int i = 0; i < S.length(); i++)
        {

            // If ans string is empty or its last
            // character does not match with the
            // current character then append this
            // character to the string
            if (ans.isEmpty() ||
                ans.charAt(ans.length() - 1) != S.charAt(i))
                ans += S.charAt(i);

            // Matches with the previous one
            else if (ans.charAt(ans.length() - 1) == S.charAt(i))
                ans = ans.substring(0, ans.length() - 1);
        }

        // Return the answer
        return ans;
    }

    // Driver Code
    public static void main(String[] args)
    {
        String str = "keexxllx";
        System.out.println(removeDuplicates(str));
    }
}

// This code is contributed by
// sanjeev2552

Python3

# Python3 implementation of the above approach

# Function to remove adjacent duplicates
def removeDuplicates(S) :

    ans = "";

    # Iterate for every character
    # in the string
    for it in S :

        # If ans string is empty or its last
        # character does not match with the
        # current character then append this
        # character to the string
        if (ans == "" or ans[-1] != it) :
            ans += it ;

        # Matches with the previous one
        elif (ans[-1] == it) :
            ans = ans[:-1];

    # Return the answer
    return ans;


# Driver Code
if __name__ == "__main__" :

    string = "keexxllx";
    print(removeDuplicates(string));

# This code is contributed by AnkitRai01

C#

// C# implementation of the above approach
using System;

class GFG
{

    // Function to remove adjacent duplicates
    static String removeDuplicates(String S)
    {
        String ans = "";

        // Iterate for every character
        // in the string
        for (int i = 0; i < S.Length; i++)
        {

            // If ans string is empty or its last
            // character does not match with the
            // current character then append this
            // character to the string
            if (ans == "" ||
                ans[ans.Length - 1] != S[i])
                ans += S[i];

            // Matches with the previous one
            else if (ans[ans.Length - 1] == S[i])
                ans = ans.Substring(0, ans.Length - 1);
        }

        // Return the answer
        return ans;
    }

    // Driver Code
    public static void Main(String[] args)
    {
        String str = "keexxllx";
        Console.WriteLine(removeDuplicates(str));
    }
}

// This code is contributed by Rajput-Ji

Javascript

<script>

// JavaScript implementation of the above approach

// Function to remove adjacent duplicates
     function removeDuplicates( S) {
        var ans = "";

        // Iterate for every character
        // in the string
        for (i = 0; i < S.length; i++) {

            // If ans string is empty or its last
            // character does not match with the
            // current character then append this
            // character to the string
            if (ans.length==0 ||
            ans.charAt(ans.length - 1) != S.charAt(i))
                ans += S.charAt(i);

            // Matches with the previous one
            else if (ans.charAt(ans.length - 1) == S.charAt(i))
                ans = ans.substring(0, ans.length - 1);
        }

        // Return the answer
        return ans;
    }

    // Driver Code

        var str = "keexxllx";
        document.write(removeDuplicates(str));

// This code contributed by Rajput-Ji

</script>

Output:

kx

Time Complexity: O(N), as we are using a loop to traverse N times. Where N is the length of the string.

Auxiliary Space: O(N), as we are using extra space for the ans string. Where N is the length of the string.