You initialize an array to hold the complete substring of ASCII characters. You then use an array and a counter in a for loop to recursively go through the substring. Inside the for loop you are reading each element I in the array. When it is read you can use the regex match to see if the substring character in that array slot is an ASCII or NONASCII characters and if it is true it returns the value and if not and it is false you do not return the NONASCII character. You then loop through the array until it ends. Now for me I had technology related issues to use HackerRank so I explained this process in full granular detail to my interviewers which they deemed acceptable and I still did not get the job.