I did my homework and research on company and interview questions etc. I am an active member of Hacker rank since a year now, I have practiced quite enough to know how stuff works on "hackerrank" challenges. So I was expecting this problem(not exactly in same manner but similar applied concept). After a little trial and error it took me about 50 mins to figure out and code the correct answer which will pass all test cases. On hackerrank, your code is not only tested on one input set but several of them. I am very positive that my code passed all the 8-9 test cases.