Write a C++ function lefties which returns the number of left child nodes in a node-based binary search tree containing positive integers. For example, given the binary search tree below, your function should return 4 , because it contains 4 nodes which are left children - nodes 1,2,3, and 7 . Assume each node in your tree is implemented using the class BinaryNode, which implements the following binary node functions discussed in the videos and textbool (and only the following functions). +getItem(): integer +isLeaf (): boolean +getLeftChildPtr(): BinaryNode* +getRightChildPtr() : BinaryNode* // nodePtr: pointer to the root node of tree to check int lefties (BinaryNode* nodePtr)