This question looks really familiar. Friend of yours? Classmate? That question seems to indicate that you are looking for a recursive solution, and that rev_N can appear in any sub-path, and that you would only want to retain the path that has the highest rev_N in it. Can you confirm your need? Can you describe how you would solve this if you had a pencil and paper? It's often useful to separate the code-implementation from the algorithm. Once the algorithm is understood, then committing it to code often becomes easier.