Regular Expressions to Validate Provident Fund(PF) Account Number

Given some PF(Provident Fund) Account Number, the task is to check if they are valid or not using regular expressions. Rules for the valid PF Account Number are :

• PF account number is alphanumeric String and forward slaces.
• First five characters are reserved for alphabet letters.
• Next 17 characters are reserved for digits(0-9).
• It allows only special characters whitespaces and forward slaces.
• Its length should be less than equal to if: 
  • It contains forward slaces: 26
  • It contains whitespaces: 26.
  • It does not contain forward slaces and whitespaces: 22

Examples:

Input: str =  "TN MAS 1207199 123 1234567"
Output: True

Input: str = "TN/MAS/1207199/123"
Output: False

Approach: The problem can be solved based on the following idea:

Create a regex pattern to validate the number as written below:   
regex = "^[A-Z]{2}[\s\/]?[A-Z]{3}[\s\/]?[0-9]{7}[\s\/]?[0-9]{3}[\s\/]?[0-9]{7}$"

Where,

• ^: Start of the string
• [A-Z]{2}: 2 alphabets characters should be there.
• [\s\/]  : Either space or forward slace
• [0-9]{3} : 3 digits should  be there.

Follow the below steps to implement the idea:

• Create a regex expression forPF Account Number.
• Use Pattern class to compile the regex formed.
• Use the matcher function to check whether the Account Number is valid or not.
• If it is valid, return true. Otherwise, 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)  

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