URLify a given string (Replace spaces with %20)

Write a method to replace all the spaces in a string with ‘%20’. You may assume that the string has sufficient space at the end to hold the additional characters and that you are given the “true” length of the string.
Examples:

Input: "Mr John Smith", 13
Output: Mr%20John%20Smith

Input: "Mr John Smith   ", 13
Output: Mr%20John%20Smith

A simple solution is to create an auxiliary string and copy characters one by one. Whenever space is encountered, place %20 in place of it.

A better solution to do in-place assuming that we have extra space in the input string. We first count the number of spaces in the input string. Using this count, we can find the length of the modified (or result) string. After computing the new length we fill the string in-place from the end. 

Below is the implementation of the above approach:

C++

// C++ program to replace spaces with %20
#include<stdio.h>

// Maximum length of string after modifications.
const int MAX = 1000;

// Replaces spaces with %20 in-place and returns
// new length of modified string. It returns -1
// if modified string cannot be stored in str[]
int replaceSpaces(char str[])
{
    // count spaces and find current length
    int space_count = 0, i;
    for (i = 0; str[i]; i++)
        if (str[i] == ' ')
            space_count++;

    // Remove trailing spaces
    while (str[i-1] == ' ')
    {
       space_count--;
       i--;
    }

    // Find new length.
    int new_length = i + space_count * 2 + 1;

    // New length must be smaller than length
    // of string provided.
    if (new_length > MAX)
        return -1;

    // Start filling character from end
    int index = new_length - 1;

    // Fill string termination.
    str[index--] = '\0';

    // Fill rest of the string from end
    for (int j=i-1; j>=0; j--)
    {
        // inserts %20 in place of space
        if (str[j] == ' ')
        {
            str[index] = '0';
            str[index - 1] = '2';
            str[index - 2] = '%';
            index = index - 3;
        }
        else
        {
            str[index] = str[j];
            index--;
        }
    }

    return new_length;
}

// Driver code
int main()
{
    char str[MAX] = "Mr John Smith   ";

    // Prints the replaced string
    int new_length = replaceSpaces(str);
    for (int i=0; i<new_length; i++)
        printf("%c", str[i]);
    return 0;
}

Java

// Java program to replace spaces with %20
class GFG
{

    // Maximum length of string
    // after modifications.
    static int MAX = 1000;

    // Replaces spaces with %20 in-place
    // and returns new length of modified string.
    // It returns -1 if modified string
    // cannot be stored in str[]
    static char[] replaceSpaces(char[] str)
    {

        // count spaces and find current length
        int space_count = 0, i = 0;
        for (i = 0; i < str.length; i++)
            if (str[i] == ' ')
                space_count++;

        // count spaces and find current length
        while (str[i - 1] == ' ')
        {
            space_count--;
            i--;
        }

        // Find new length.
        int new_length = i + space_count * 2;

        // New length must be smaller than length
        // of string provided.
        if (new_length > MAX)
            return str;

        // Start filling character from end
        int index = new_length - 1;

        char[] old_str = str;
        str = new char[new_length];

        // Fill rest of the string from end
        for (int j = i - 1; j >= 0; j--)
        {

            // inserts %20 in place of space
            if (old_str[j] == ' ')
            {
                str[index] = '0';
                str[index - 1] = '2';
                str[index - 2] = '%';
                index = index - 3;
            }

            else
            {
                str[index] = old_str[j];
                index--;
            }
        }
        return str;
    }

    // Driver Code
    public static void main(String[] args)
    {
        char[] str = "Mr John Smith ".toCharArray();

        // Prints the replaced string
        str = replaceSpaces(str);

        for (int i = 0; i < str.length; i++)
            System.out.print(str[i]);
    }
}

// This code is contributed by
// sanjeev2552

Python3

# Maximum length of string after modifications.
MAX = 1000;

# Replaces spaces with %20 in-place and returns
# new length of modified string. It returns -1
# if modified string cannot be stored in str[]
def replaceSpaces(string):

    # Remove remove leading and trailing spaces
    string = string.strip()

    i = len(string)

    # count spaces and find current length
    space_count = string.count(' ')

    # Find new length.
    new_length = i + space_count * 2

    # New length must be smaller than length
    # of string provided.
    if new_length > MAX:
        return -1

    # Start filling character from end
    index = new_length - 1

    string = list(string)

    # Fill string array
    for f in range(i - 2, new_length - 2):
        string.append('0')

    # Fill rest of the string from end
    for j in range(i - 1, 0, -1):

        # inserts %20 in place of space
        if string[j] == ' ':
            string[index] = '0'
            string[index - 1] = '2'
            string[index - 2] = '%'
            index = index - 3
        else:
            string[index] = string[j]
            index -= 1

    return ''.join(string)

# Driver Code
if __name__ == '__main__':
    s = "Mr John Smith "
    s = replaceSpaces(s)
    print(s)

# This code is contributed by Vinayak

C#

// C# program to replace spaces with %20
using System;

class GFG
{

    // Maximum length of string
    // after modifications.
    static int MAX = 1000;

    // Replaces spaces with %20 in-place
    // and returns new length of modified string.
    // It returns -1 if modified string
    // cannot be stored in []str
    static char[] replaceSpaces(char[] str)
    {

        // count spaces and find current length
        int space_count = 0, i = 0;
        for (i = 0; i < str.Length; i++)
            if (str[i] == ' ')
                space_count++;

        // count spaces and find current length
        while (str[i - 1] == ' ')
        {
            space_count--;
            i--;
        }

        // Find new length.
        int new_length = i + space_count * 2;

        // New length must be smaller than
        // length of string provided.
        if (new_length > MAX)
            return str;

        // Start filling character from end
        int index = new_length - 1;

        char[] new_str = str;
        str = new char[new_length];

        // Fill rest of the string from end
        for (int j = i - 1; j >= 0; j--)
        {

            // inserts %20 in place of space
            if (new_str[j] == ' ')
            {
                str[index] = '0';
                str[index - 1] = '2';
                str[index - 2] = '%';
                index = index - 3;
            }
            else
            {
                str[index] = new_str[j];
                index--;
            }
        }
        return str;
    }

    // Driver Code
    public static void Main(String[] args)
    {
        char[] str = "Mr John Smith ".ToCharArray();

        // Prints the replaced string
        str = replaceSpaces(str);

        for (int i = 0; i < str.Length; i++)
            Console.Write(str[i]);
    }
}

// This code is contributed by 29AjayKumar

Output:

Mr%20John%20Smith

Time Complexity: O(n), where n is the true length of the string. 
Auxiliary Space: O(1), because the above program is an inplace algorithm.

Approach 2: 
Trim the string and call replaceAll() method, to replace all space Unicode to %20. 

Below is the implementation of the above approach:

Java

// Java implementation of above approach
class GFG
{
    public static void main(String[] args)
    {
        // Instantiate the string
        String str = "Mr John Smith   ";

        // Trim the given string
        str = str.trim();

        // Replace All space (unicode is \\s) to %20
        str = str.replaceAll("\\s", "%20");

        // Display the result
        System.out.println(str);
    }
}

Python3

# Python3 implementation of above approach

# Instantiate the string
s = "Mr John Smith "

# Trim the given string
s = s.strip()

# Replace All space (unicode is \\s) to %20
s = s.replace(' ', "%20")

# Display the result
print(s)

# This code is contributed by vinayak

C#

// C# implementation of above approach
using System;

class GFG
{
    public static void Main()
    {
        // Instantiate the string
        String str = "Mr John Smith   ";

        // Trim the given string
        str = str.Trim();

        // Replace All space (unicode is \\s) to %20
        str = str.Replace(" ", "%20");

        // Display the result
        Console.Write(str);
    }
}

// This code is contributed by Rajput-Ji

Javascript

<script>

      // JavaScript implementation of above approach

      // Instantiate the string
      var str = "Mr John Smith ";

      // Trim the given string
      str = str.trim();

      // Replace All space (unicode is \\s) to %20
      str = str.replaceAll(" ", "%20");

      // Display the result
      document.write(str);

</script>

Output:

Mr%20John%20Smith

Approach 3: using string.replace() function :

Below is the implementation of the above approach:

C++

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

void replaceSpaces(string input)
{
    string rep = "%20";
    for(int i=0 ; i<input.length() ; i++)
    {
        if(input[i] == ' ')
            input.replace(i,1,rep);
    }
    cout<<input;
}

int main()
{
    string input = "Mr John Smith";
    replaceSpaces(input);

    return 0;
}

Python3

#Python code for the same approach
def replaceSpaces(input):
    rep = "%20"
    for i in range(len(input)):
        if(input[i] == ' '):
            input = input.replace(input[i],rep)
    print(input)

# driver code
input = "Mr John Smith"
replaceSpaces(input)

# This code is contributed by shinjanpatra

Javascript

<script>

// JavaScript code for the approach
function replaceSpaces(input)
{
    let rep = "%20"
    for(let i=0 ; i<input.length ; i++)
    {
        if(input[i] == ' ')
            input = input.replace(input[i],rep);
    }
    document.write(input);
}

// driver code
let input = "Mr John Smith"
replaceSpaces(input)

// This code is contributed by shinjanpatra

</script>

Output:

Mr%20John%20Smith

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