How to validate MAC address using Regular Expression

Given string str, the task is to check whether the given string is a valid MAC address or not by using Regular Expression.

A valid MAC address must satisfy the following conditions: 

1. It must contain 12 hexadecimal digits.
2. One way to represent them is to form six pairs of the characters separated with a hyphen (-) or colon(:). For example, 01-23-45-67-89-AB is a valid MAC address.
3. Another way to represent them is to form three groups of four hexadecimal digits separated by dots(.). For example, 0123.4567.89AB is a valid MAC address.

Examples: 

Input: str = "01-23-45-67-89-AB"; 
Output: true 
Explanation: 
The given string satisfies all the above mentioned conditions. Therefore, it is a valid MAC address.

Input: str = "01-23-45-67-89-AH"; 
Output: false 
Explanation: 
The given string contains 'H', the valid hexadecimal digits should be followed by letter from a-f, A-F, and 0-9. Therefore, it is not a valid MAC address.

Input: str = "01-23-45-67-AH"; 
Output: false 
Explanation: 
The given string has five groups of two hexadecimal digits. Therefore, it is not a valid MAC address. 
 

Approach: The idea is to use Regular Expression to solve this problem. The following steps can be followed to compute the answer. 

• Get the String.
• Create a regular expression to check valid MAC address as mentioned below:

regex = "^([0-9A-Fa-f]{2}[:-]){5}([0-9A-Fa-f]{2})|([0-9a-fA-F]{4}\\.[0-9a-fA-F]{4}\\.[0-9a-fA-F]{4})$"; 

• Where: 
  
  • ^ represents the starting of the string.
  • ([0-9A-Fa-f]{2}[:-]){5} represents the five groups of two hexadecimal digits separated by hyphens (-) or colons (:)
  • ([0-9A-Fa-f]{2}) represents the one groups of two hexadecimal digits.
  • | represents the or.
  • ( represents the starting of the group.
  • [0-9a-fA-F]{4}\\. represents the first part of four hexadecimal digits separated by dots (.).
  • [0-9a-fA-F]{4}\\. represents the second part of four hexadecimal digits separated by dots (.).
  • [0-9a-fA-F]{4} represents the third part of four hexadecimal digits.
  • ) represents the ending of the group.
  • $ represents the ending of the string.
• Match the given string with the Regular Expression. In Java, this can be done by using Pattern.matcher().
• Return true if the string matches with the given regular expression, else return false.

Below is the implementation of the above approach:

true
true
true
false
false

Time Complexity: O(N) for each testcase, where N is the length of the given string. 
Auxiliary Space: O(1)