Your task is to compute a set of all path lengths in a binary tree. For example, given this tree,

you should return the set {1, 3, 5 } because there are paths of length 1, 3, and 5 in this set. A path is a sequence of nodes starting from the root. The length of a path is the number of arrows in the figure, or equivalently, the number of nodes - 1.

You need to complete the recursive pathLengths method in the class below.