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 textboc

$($and only the following functions$).$