URLify a given string (Replace spaces is %20)

• Difficulty Level : Medium
• Last Updated : 10 Jun, 2021

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 // 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 codeint main(){    char str[MAX] = "Mr John Smith   ";     // Prints the replaced string    int new_length = replaceSpaces(str);    for (int i=0; i

Java

 // Java program to replace spaces with %20class 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 Codeif __name__ == '__main__':    s = "Mr John Smith "    s = replaceSpaces(s)    print(s) # This code is contributed by Vinayak

C#

 // C# program to replace spaces with %20using 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 approachclass 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 strings = "Mr John Smith " # Trim the given strings = s.strip() # Replace All space (unicode is \\s) to %20s = s.replace(' ', "%20") # Display the resultprint(s) # This code is contributed by vinayak

C#

 // C# implementation of above approachusing 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



Output:

Mr%20John%20Smith

Approach 3: using string.replace() function :

Below is the implementation of the above approach:

C++

 #include using namespace std; void replaceSpaces(string input){    string rep = "%20";    for(int i=0 ; i

Output:

Mr%20John%20Smith

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