Check if a given string is a valid Hexadecimal Color Code or not

Given a string str, the task is to check whether the given string is an HTML Hex Color Code or not. Print Yes if it is, otherwise print No.

Examples:

Input: str = “#1AFFa1”
Output: Yes

Input: str = “#F00”
Output: Yes

Input: str = “123456”
Output: No

Approach:  An HTML Hex Color Code follows the below-mentioned set of rules: 

1. It starts with the ‘#’ symbol.
2. Then it is followed by the letters from a-f, A-F and/or digits from 0-9.
3. The length of the hexadecimal color code should be either 6 or 3, excluding ‘#’ symbol.
4. For example: #abc, #ABC, #000, #FFF, #000000, #FF0000, #00FF00, #0000FF, #FFFFFF are all valid Hexadecimal color codes.

Now, to solve the above problem follow the below steps:

1. Check the string str for the following conditions:
   • If the first character is not #, return false.
   • If the length is not 3 or 6. If not, return false.
   • Now, check for all characters other than the first character that are 0-9, A-F or a-f.
2. If all the conditions mentioned above are satisfied, then return true.
3. Print answer according to the above observation.

Below is the implementation of the above approach:

CPP

// C++ program for the above approach

#include <iostream>
using namespace std;

// Function to validate
// the HTML hexadecimal color code.
bool isValidHexaCode(string str)
{
    if (str[0] != '#')
        return false;

    if (!(str.length() == 4 or str.length() == 7))
        return false;

    for (int i = 1; i < str.length(); i++)
        if (!((str[i] >= '0' && str[i] <= 9)
              || (str[i] >= 'a' && str[i] <= 'f')
              || (str[i] >= 'A' || str[i] <= 'F')))
            return false;

    return true;
}

// Driver Code
int main()
{
    string str = "#1AFFa1";

    if (isValidHexaCode(str)) {
        cout << "Yes" << endl;
    }
    else {
        cout << "No" << endl;
    }
    return 0;
}

Java

// Java program for the above approach
import java.util.*;
class GFG{

    // Function to validate
    // the HTML hexadecimal color code.
    static boolean isValidHexaCode(String str)
    {
        if (str.charAt(0) != '#')
            return false;

        if (!(str.length() == 4 || str.length() == 7))
            return false;

        for (int i = 1; i < str.length(); i++)
            if (!((str.charAt(i) >= '0' && str.charAt(i) <= 9)
                || (str.charAt(i) >= 'a' && str.charAt(i) <= 'f')
                || (str.charAt(i) >= 'A' || str.charAt(i) <= 'F')))
                return false;

        return true;
    }

    // Driver code
    public static void main(String args[])
    {
        String str = "#1AFFa1";

        if (isValidHexaCode(str)) {
            System.out.println("Yes");
        }
        else {
            System.out.println("No");
        }
    }
}

// This code is contributed by Samim Hossain Mondal.

Python3

# python program for the above approach

# Function to validate
# the HTML hexadecimal color code.
def isValidHexaCode(str):

    if (str[0] != '#'):
        return False

    if (not(len(str) == 4 or len(str) == 7)):
        return False

    for i in range(1, len(str)):
        if (not((str[i] >= '0' and str[i] <= '9') or (str[i] >= 'a' and str[i] <= 'f') or (str[i] >= 'A' or str[i] <= 'F'))):
            return False

    return True


# Driver Code
if __name__ == "__main__":

    str = "#1AFFa1"

    if (isValidHexaCode(str)):
        print("Yes")

    else:
        print("No")

    # This code is contributed by rakeshsahni

C#

// C# program for the above approach
using System;
class GFG{

    // Function to validate
    // the HTML hexadecimal color code.
    static bool isValidHexaCode(string str)
    {
        if (str[0] != '#')
            return false;

        if (!(str.Length == 4 || str.Length == 7))
            return false;

        for (int i = 1; i < str.Length; i++)
            if (!((str[i] >= '0' && str[i] <= 9)
                || (str[i] >= 'a' && str[i] <= 'f')
                || (str[i] >= 'A' || str[i] <= 'F')))
                return false;

        return true;
    }

    // Driver code
    public static void Main()
    {
        string str = "#1AFFa1";

        if (isValidHexaCode(str)) {
            Console.Write("Yes");
        }
        else {
            Console.Write("No");
        }
    }
}
// This code is contributed by Samim Hossain Mondal.

Javascript

<script>
       // JavaScript Program to implement
       // the above approach

       // Function to validate
       // the HTML hexadecimal color code.
       function isValidHexaCode(str) {
           if (str[0] != '#')
               return false;

           if (!(str.length == 4 || str.length == 7))
               return false;

           for (let i = 1; i < str.length; i++)
               if (!((str[i].charCodeAt(0) <= '0'.charCodeAt(0) && str[i].charCodeAt(0) <= 9)
                   || (str[i].charCodeAt(0) >= 'a'.charCodeAt(0) && str[i].charCodeAt(0) <= 'f'.charCodeAt(0))
                   || (str[i].charCodeAt(0) >= 'A'.charCodeAt(0) || str[i].charCodeAt(0) <= 'F'.charCodeAt(0))))
                   return false;

           return true;
       }

       // Driver Code
       let str = "#1AFFa1";

       if (isValidHexaCode(str)) {
           document.write("Yes" + '<br>');
       }
       else {
           document.write("No" + '<br>');
       }

   // This code is contributed by Potta Lokesh
   </script>

Output

Yes

Time Complexity: O(N)
Auxiliary Space: O(1)

Approach 2: Regex Expression:

In this approach, we have used regex library to define a regular expression pattern to match the HTML hexadecimal color code. The regular expression pattern ^#([a-fA-F0-9]{6}|[a-fA-F0-9]{3})$ matches the string that starts with # and followed by either 6 hexadecimal digits or 3 hexadecimal digits. The regex_match function checks if the given string matches the regular expression pattern or not, and returns true if it matches, else false.

Here is the code given below:

C++

#include <iostream>
#include <regex>
using namespace std;

// Function to validate
// the HTML hexadecimal color code using regex.
bool isValidHexaCode(string str)
{
    regex hexaCode("^#([a-fA-F0-9]{6}|[a-fA-F0-9]{3})$");
    return regex_match(str, hexaCode);
}

// Driver Code
int main()
{
    string str = "#1AFFa1";

    if (isValidHexaCode(str)) {
        cout << "Yes" << endl;
    }
    else {
        cout << "No" << endl;
    }
    return 0;
}

Output

Yes

Time Complexity: O(N)
Auxiliary Space: O(1)