String after processing backspace characters

Last Updated : 07 Sep, 2022

Given a string S containing letters and '#'. The '#" represents a backspace. The task is to print the new string without '#'.

Examples:

Input : S = "abc#de#f#ghi#jklmn#op#"
Output : abdghjklmo

Input : S = "##geeks##for##geeks#"
Output : geefgeek

Approach: A simple approach to this problem by using deque is as follows:

Traverse the string S.
If any character except '#' is found push it at back in deque.
if the character '#' is found pop a character from back of deque.
Finally pop all elements from front of deque to make new string.

Below is the implementation of above approach:

C++

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

// Function to find new final String
string newString(string S)
{
    deque<char> q;

    for (int i = 0; i < S.length(); ++i) {

        if (S[i] != '#')
            q.push_back(S[i]);
        else if (!q.empty())
            q.pop_back();
    }

    // build final string
    string ans = "";

    while (!q.empty()) {
        ans += q.front();
        q.pop_front();
    }

    // return final string
    return ans;
}

// Driver program
int main()
{
    string S = "##geeks##for##geeks#";

    // function call to print required answer
    cout << newString(S);

    return 0;
}

// This code is contributed by Sanjit_Prasad

Java

// Java implementation of above approach 
import java.util.*;
class GFG 
{

// Function to find new final String 
static String newString(String S) 
{ 
    Stack<Character> q = new Stack<Character>(); 

    for (int i = 0; i < S.length(); ++i) 
    { 
        if (S.charAt(i) != '#') 
            q.push(S.charAt(i)); 
        else if (!q.isEmpty()) 
            q.pop(); 
    } 

    // build final string 
    String ans = ""; 

    while (!q.isEmpty())
    { 
        ans += q.pop(); 
    } 

    // return final string 
    String answer = "";
    for(int j = ans.length() - 1; j >= 0; j--)
    {
        answer += ans.charAt(j);
    }
    return answer; 
} 

// Driver Code 
public static void main(String[] args) 
{ 
    String S = "##geeks##for##geeks#"; 

    // function call to print 
    // required answer 
    System.out.println(newString(S)); 
}
} 

// This code is contributed
// by prerna saini

Python3

# Python3 implementation of above approach 

# Function to find new final String 
def newString(S): 
    
    q = [] 

    for i in range(0, len(S)): 

        if S[i] != '#': 
            q.append(S[i]) 
        elif len(q) != 0: 
            q.pop() 

    # Build final string 
    ans = "" 

    while len(q) != 0: 
        ans += q[0] 
        q.pop(0) 

    # return final string 
    return ans 

# Driver Code
if __name__ == "__main__": 

    S = "##geeks##for##geeks#"

    # Function call to print 
    # required answer 
    print(newString(S))
    
# This code is contributed by Rituraj Jain

// C# implementation of above approach 
using System.Collections.Generic;
using System;

class GFG 
{

// Function to find new final String 
static String newString(String S) 
{ 
    Stack<Char> q = new Stack<Char>(); 

    for (int i = 0; i < S.Length; ++i) 
    { 
        if (S[i] != '#') 
            q.Push(S[i]); 
        else if (q.Count!=0) 
            q.Pop(); 
    } 

    // build final string 
    String ans = ""; 

    while (q.Count!=0)
    { 
        ans += q.Pop(); 
    } 

    // return final string 
    String answer = "";
    for(int j = ans.Length - 1; j >= 0; j--)
    {
        answer += ans[j];
    }
    return answer; 
} 

// Driver Code 
public static void Main(String []args) 
{ 
    String S = "##geeks##for##geeks#"; 

    // function call to print 
    // required answer 
    Console.WriteLine(newString(S)); 
}
}

// This code is contributed by 29AjayKumar

JavaScript

<script>
// Javascript implementation of above approach 

// Function to find new final String 
function newString(S)
{
    let q = [];
  
    for (let i = 0; i < S.length; ++i) 
    { 
        if (S[i] != '#') 
            q.push(S[i]); 
        else if (q.length!=0) 
            q.pop(); 
    } 
  
    // build final string 
    let ans = ""; 
  
    while (q.length!=0)
    { 
        ans += q.pop(); 
    } 
  
    // return final string 
    let answer = "";
    for(let j = ans.length - 1; j >= 0; j--)
    {
        answer += ans[j];
    }
    return answer; 
}

// Driver Code 
let S = "##geeks##for##geeks#"; 

// function call to print 
// required answer 
document.write(newString(S)+"<br>"); 

// This code is contributed by rag2127
</script>

Output

geefgeek

Complexity Analysis:

Time Complexity: O(N), where N is the length of the String.
Space Complexity: O(N) since using auxiliary deque

Reverse a string without affecting special characters

Sanjit_Prasad

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String after processing backspace characters

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