Phone Number Digit check

Handle phone number check based on the digit.

##Features:

• Check if the valid_word matched with the digit
• Check if there are any duplicate
• Able to check if there are upper case
• Added validation for the input param
• Unit testing for every functionality & negative test case

##Complexity:

time complexity: O(N * M)

N -> total size of valid words M -> maximum length of the valid word Time complexity is because of the loop for every single words O(N) and check every single letter inside the word O(M)

space complexity O(N)

Adding new hashset to handle duplicate words

How to run

• Clone the repo
• Check testFile TestPhoneNumberCheck
• Check testGetMatchingWords and modified it to test the functionality