Replace all occurrences of a string with space

Last Updated : 16 Sep, 2023

Given a string and a substring, the task is to replace all occurrences of the substring with space. We also need to remove trailing and leading spaces created due to this.

Examples:

Input: str = "LIELIEILIEAMLIECOOL", sub = "LIE"
Output: I AM COOL By replacing all occurrences of Sub in Str with empty spaces, we extract the secret message as I AM COOL.

Input: str = "XYZAXYZBXYZC", sub = "XYZ"
Output: ABC By replacing all occurrences of Sub in Str with empty spaces, we extract the secret message as ABC.

Approach:

In the given string Str, replace all occurrences of Sub with empty spaces.
Remove unwanted empty spaces in start and end of the string.
Print the modified string.

Below is the implementation of the above approach:

C++

// C++ implementation to extract 
// the secret message
#include <bits/stdc++.h>
using namespace std;

// Trim method implementation to remove 
// trailing and leading white-spaces
string trim(const string &s)
{
    auto start = s.begin();
    while (start != s.end() && 
           isspace(*start))
        start++;

    auto end = s.end();
    do
    {
        end--;
    } while (distance(start, end) > 0 && 
                    isspace(*end));

    return string(start, end + 1);
}

// Function to extract the secret message
string extractSecretMessage(string str, 
                            string sub)
{
    // Replacing all occurrences of
    // Sub in Str by empty spaces
    size_t pos;
    while ((pos = str.find(sub)) != string::npos)
        str.replace(pos, 3, " ");

    // Removing unwanted spaces in the
    // start and end of the string
    str = trim(str);

    return str;
}

// Driver code
int main(int argc, char const *argv[])
{
    string str = "LIELIEILIEAMLIECOOL";
    string sub = "LIE";
    cout << extractSecretMessage(str, sub) 
         << endl;
    return 0;
}

// This code is contributed by
// sanjeev2552

Java

// Java implementation to extract the secret message
import java.io.*;
import java.util.*;

class GFG {

    // Function to extract the secret message
    static String extractSecretMessage(String Str, String Sub)
    {
        // Replacing all occurrences of
        // Sub in Str by empty spaces
        Str = Str.replaceAll(Sub, " ");

        // Removing unwanted spaces in the
        // start and end of the string
        Str = Str.trim();

        return Str;
    }

    // Driver code
    public static void main(String args[])
    {
        String Str = "LIELIEILIEAMLIECOOL";
        String Sub = "LIE";
        System.out.println(extractSecretMessage(Str, Sub));
    }
}

Python3

# Python3 implementation to extract
# the secret message

# Function to extract the secret message
def extractSecretMessage(Str, Sub):

    # Replacing all occurrences of
    # Sub in Str by empty spaces
    Str= Str.replace(Sub, " ")

    # Removing unwanted spaces in the
    # start and end of the string
    
    return Str.strip()

# Driver code
Str = "LIELIEILIEAMLIECOOL"
Sub = "LIE"
print(extractSecretMessage(Str, Sub))

# This code is contributed 
# by ihritik

// C# implementation to extract the 
// secret message 
using System;

class GFG 
{ 

// Function to extract the secret message 
static string extractSecretMessage(string Str, 
                                   string Sub) 
{ 
    // Replacing all occurrences of 
    // Sub in Str by empty spaces 
    Str = Str.Replace(Sub, " "); 

    // Removing unwanted spaces in the 
    // start and end of the string 
    Str = Str.Trim(); 

    return Str; 
} 

// Driver code 
public static void Main() 
{ 
    string Str = "LIELIEILIEAMLIECOOL"; 
    string Sub = "LIE"; 
    Console.WriteLine(extractSecretMessage(Str, Sub)); 
} 
} 

// This code is contributed by Ryuga

JavaScript

//  Javascript implementation to extract
//  the secret message

//  Function to extract the secret message
function extractSecretMessage(Str, Sub) {

    //  Replacing all occurrences of
    //  Sub in Str by empty spaces
    let i = 0, n = Str.length;
    let k = Sub.length;
    while(i < n) {
        Str = (Str.replace(Sub, " "));
        i += k;
    }

    // Removing unwanted spaces in the
    // start and end of the string
    return Str.trim();
}

//  Driver code
let Str = " LIELIEILIEAMLIECOOL";
let Sub = "LIE";
console.log(extractSecretMessage(Str, Sub));

//  This code is contributed 
//  by Samim Hossain Mondal

PHP

<?php
// PHP implementation to extract the 
// secret message

// Function to extract the secret message
function extractSecretMessage($Str, $Sub)
{
    // Replacing all occurrences of
    // Sub in Str by empty spaces
    $Str = str_replace($Sub, " ", $Str);

    // Removing unwanted spaces in the
    // start and end of the string
    
    return trim($Str);
}

// Driver code
$Str = "LIELIEILIEAMLIECOOL";
$Sub = "LIE";
echo extractSecretMessage($Str, $Sub);

// This code is contributed 
// by ihritik
?>

Output

I AM COOL

Complexity Analysis:

Time Complexity: O(N), as we are using replace function which will cost us O(N) time.
Auxiliary Space: O(1), as we are not using any extra space.

Approach:

Initialize an empty string called result.
Loop through the input string str, and for each character.
Check if the current character is the same as the first character of the substring sub. If so, check if the next characters match with the substring. If there is a match, skip the characters that match with the substring and add a space to the result string.
If the current character is not the same as the first character of the substring, add it to the result string.
Trim the result string to remove leading and trailing spaces.
Return the result string.

Below is the implementation of the above approach:

C++

#include <bits/stdc++.h>
using namespace std;

string extractSecretMessage(string str, string sub) {
    string result;
    int n = str.length(), m = sub.length(), i = 0;

    while (i < n) {
        if (str[i] == sub[0] && str.substr(i, m) == sub) {
            result += " ";
            i += m;
        } else {
            result += str[i];
            i++;
        }
    }

    // Trim the result string
    auto start = result.begin();
    while (start != result.end() && isspace(*start))
        start++;

    auto end = result.end();
    do {
        end--;
    } while (distance(start, end) > 0 && isspace(*end));

    return string(start, end + 1);
}

int main() {
    string str = "LIELIEILIEAMLIECOOL";
    string sub = "LIE";
    cout << extractSecretMessage(str, sub) << endl; // Output: I AM COOL
    return 0;
}

Java

import java.util.*;

public class Main {
    public static void main(String[] args) {
        String str = "LIELIEILIEAMLIECOOL";
        String sub = "LIE";
        System.out.println(extractSecretMessage(str, sub)); // Output: I AM COOL
    }

    // Function to extract the secret message from a given string 'str' by removing all occurrences of 'sub'
    public static String extractSecretMessage(String str, String sub) {
        StringBuilder result = new StringBuilder(); // Initialize an empty StringBuilder to store the extracted secret message
        int n = str.length(); // Get the length of the input string 'str'
        int m = sub.length(); // Get the length of the substring 'sub' we want to remove from 'str'
        int i = 0; // Initialize a pointer 'i' to traverse through the input string 'str'

        // Loop through the input string 'str'
        while (i < n) {
            // Check if the current character matches the first character of the substring 'sub'
            // and if the remaining substring from the current position has enough characters to match 'sub'
            if (str.charAt(i) == sub.charAt(0) && i + m <= n && str.substring(i, i + m).equals(sub)) {
                result.append(" "); // If a match is found, append a space to the result (to separate words)
                i += m; // Move the pointer 'i' to skip the substring 'sub' in 'str'
            } else {
                // If no match is found, append the current character from 'str' to the result
                result.append(str.charAt(i));
                i++; // Move the pointer 'i' to the next character in 'str'
            }
        }

        // Convert the result StringBuilder to a String and remove any leading or trailing spaces
        String trimmedResult = result.toString().trim();

        // Return the extracted secret message
        return trimmedResult;
    }
}

Python3

def extract_secret_message(s, sub):
    result = []  # Initialize an empty list to store the extracted secret message
    n = len(s)  # Get the length of the input string 's'
    m = len(sub)  # Get the length of the substring 'sub' we want to remove from 's'
    i = 0  # Initialize a pointer 'i' to traverse through the input string 's'

    # Loop through the input string 's'
    while i < n:
        # Check if the current character matches the first 
        # character of the substring 'sub'
        # and if the remaining substring from the current 
        # position has enough characters to match 'sub'
        if s[i] == sub[0] and i + m <= n and s[i:i + m] == sub:
            # If a match is found, append a space to the result (to separate words)
            result.append(" ")
            i += m  # Move the pointer 'i' to skip the substring 'sub' in 's'
        else:
            # If no match is found, append the current character from 's' to the result
            result.append(s[i])
            i += 1  # Move the pointer 'i' to the next character in 's'

    # Convert the result list to a string and remove any leading or trailing spaces
    trimmed_result = ''.join(result).strip()

    # Return the extracted secret message
    return trimmed_result


# Test case
str_input = "LIELIEILIEAMLIECOOL"
sub_input = "LIE"
print(extract_secret_message(str_input, sub_input))  # Output: "I AM COOL"

using System;
using System.Text;

public class GFG
{
    public static void Main(string[] args)
    {
        string str = "LIELIEILIEAMLIECOOL";
        string sub = "LIE";
        Console.WriteLine(ExtractSecretMessage(str, sub)); // Output: I AM COOL
    }

    // Function to extract the secret message from a given string 'str' by removing all occurrences of 'sub'
    public static string ExtractSecretMessage(string str, string sub)
    {
        StringBuilder result = new StringBuilder(); // Initialize an empty StringBuilder to store the extracted secret message
        int n = str.Length; // Get the length of the input string 'str'
        int m = sub.Length; // Get the length of the substring 'sub' we want to remove from 'str'
        int i = 0; // Initialize a pointer 'i' to traverse through the input string 'str'

        // Loop through the input string 'str'
        while (i < n)
        {
            // Check if the current character matches the first character of the substring 'sub'
            // and if the remaining substring from the current position has enough characters to match 'sub'
            if (str[i] == sub[0] && i + m <= n && str.Substring(i, m) == sub)
            {
                result.Append(" "); // If a match is found, append a space to the result (to separate words)
                i += m; // Move the pointer 'i' to skip the substring 'sub' in 'str'
            }
            else
            {
                // If no match is found, append the current character from 'str' to the result
                result.Append(str[i]);
                i++; // Move the pointer 'i' to the next character in 'str'
            }
        }

        // Convert the result StringBuilder to a String and remove any leading or trailing spaces
        string trimmedResult = result.ToString().Trim();

        // Return the extracted secret message
        return trimmedResult;
    }
}

// This code is contributed by akshitaguprzj3

JavaScript

// Function to extract a secret message from a given string
function extractSecretMessage(str, sub) {
    let result = '';  // To store the extracted secret message
    let n = str.length;  // Length of the input string
    let m = sub.length;  // Length of the substring to search for
    let i = 0;  // Index for traversing the input string

    while (i < n) {
        if (str[i] === sub[0] && str.substring(i, i + m) === sub) {
            result += ' ';  // Add a space to separate secret words
            i += m;  // Move the index to skip the found substring
        } else {
            result += str[i];  // Append the current character to the result
            i++;  // Move to the next character
        }
    }

    // Trim the result string to remove leading and trailing spaces
    let start = 0;
    while (start < result.length && result[start] === ' ')
        start++;

    let end = result.length - 1;
    while (end >= start && result[end] === ' ')
        end--;

    // Return the trimmed secret message
    return result.substring(start, end + 1);
}

// Main function
function main() {
    let str = 'LIELIEILIEAMLIECOOL';
    let sub = 'LIE';
    console.log(extractSecretMessage(str, sub)); // Output: I AM COOL
}

// Call the main function to run the code
main();

// This code is contributed by rambabuguphka

Output

I AM COOL

Time Complexity: O(n * m), where n is the length of the input string and m is the length of the substring to be replaced. This is because we are iterating over the input string and comparing substrings of length m with the given substring.

Auxiliary Space: O(n) because we are using an additional string 'result' to store the modified string.

Replace all occurrences of a string with space

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