I tried this problem using top down approach(recursion), it worked on smaller test cases and failed on bigger, another thing was that it was giving me (answer-1) for bigger test cases, I read the hints and tried the bottom up with Kahn's and it works perfectly, another thing is that this is faster. I prefer using the top down approach as I understand it better, can i get a hint if this problem is solvable using top down and recursion(not reaching pythons limit), the way I was able to look for cycles was also much more convenient using that approach. I wanted put down my code so that I could get a review but I'm happy to email it for suggestions. Thanks