Counting Univalued Subtrees

Question

Can you count all the univalued subtrees in a binary tree, as shown in the figure below?

The Problem

We are given a binary tree. The challenge is to count all the univalued subtrees in the tree. Just to recall, a subtree is any node along with its descendants. The root and all its descendants form the entire tree. A univalued subtree is therefore a subtree in which all the nodes have the same keys. The figure below shows all the univalued subtrees of the binary tree of the previous figure.