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

Last Updated : 21 Sep, 2023

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 = �”
Output: No

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

It starts with the ‘#’ symbol.
Then it is followed by the letters from a-f, A-F and/or digits from 0-9.
The length of the hexadecimal color code should be either 6 or 3, excluding ‘#’ symbol.
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:

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.
If all the conditions mentioned above are satisfied, then return true.
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# 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; }

Java

import java.util.regex.Pattern; import java.util.regex.Matcher;  public class GFG {      // Function to check if a given string is a valid hexadecimal color code     public static boolean isValidHexaCode(String input) {         // Define the regular expression pattern for a valid hexadecimal color code         // It matches either a 6-character or 3-character code, preceded by a #         Pattern hexaPattern = Pattern.compile("^#([a-fA-F0-9]{6}|[a-fA-F0-9]{3})$");                  // Create a Matcher object to match the input against the pattern         Matcher matcher = hexaPattern.matcher(input);                  // Return true if the input matches the pattern, otherwise false         return matcher.matches();     }      public static void main(String[] args) {         String input = "#1AFFa1";          if (isValidHexaCode(input)) {             System.out.println("Yes");         } else {             System.out.println("No");         }     } }

Python3

import re  def is_valid_hexa_code(string):     hexa_code = re.compile(r'^#([a-fA-F0-9]{6}|[a-fA-F0-9]{3})$')     return bool(re.match(hexa_code, string))  if __name__ == "__main__":     string = "#1AFFa1"      if is_valid_hexa_code(string):         print("Yes")     else:         print("No")

using System; using System.Text.RegularExpressions;  class GFG {     // Function to validate the HTML hexadecimal color code using regex.     static bool IsValidHexaCode(string str)     {         // Regular expression to match a valid hexadecimal color code.         // The pattern "^#([a-fA-F0-9]{6}|[a-fA-F0-9]{3})$" checks for:         // ^        - Start of the string         // #        - The string must start with a hash character (#)         // (        - Start of the first group         // [a-fA-F0-9]{6} - Matches exactly six characters which can be any of a-f, A-F, or 0-9         // |        - OR         // [a-fA-F0-9]{3} - Matches exactly three characters which can be any of a-f, A-F, or 0-9         // )        - End of the first group         // $        - End of the string         Regex hexaCode = new Regex(@"^#([a-fA-F0-9]{6}|[a-fA-F0-9]{3})$");          // Check if the input string matches the regex pattern.         return hexaCode.IsMatch(str);     }      static void Main()     {         string str = "#1AFFa1";          if (IsValidHexaCode(str))         {             Console.WriteLine("Yes");         }         else         {             Console.WriteLine("No");         }     } }

JavaScript

function isValidHexaCode(input) {     // Define the regular expression pattern for a valid hexadecimal color code     // It matches either a 6-character or 3-character code, preceded by a #     var hexaPattern = /^#([a-fA-F0-9]{6}|[a-fA-F0-9]{3})$/;      // Test the input against the pattern using the test() method     return hexaPattern.test(input); }  var input = "#1AFFa1";  if (isValidHexaCode(input)) {     console.log("Yes"); } else {     console.log("No"); }

Output

Yes

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

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

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

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