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Language/Type: C++ binary trees pointers recursion
Author: Marty Stepp (on 2016/06/16)

Write a member function named tighten that could be added to the BinaryTree class. Your function should eliminate branch nodes that have only one child. For example, if a variable named tree stores the tree below at left, the call of tree.tighten(); should modify it to store the tree at right. The nodes that stored 28, 19, 32, and -8 have been eliminated because each had one child. When a node is removed, it is replaced by its child. This can lead to multiple replacements because the child might itself be replaced (as in 19 which is replaced by 32, replaced by 72). Free memory for any nodes that you remove.

tree after tree.tighten();
        /    \
     28        19
    /         /
  94        32
 /  \         \
65  -8         72
      \       /  \
      10    42    50
        /    \
     94        72
    /  \      /  \
  65    10  42    50

Constraints: Do not construct any new BinaryTreeNode objects in solving this problem (though you may create as many BinaryTreeNode* pointer variables as you like). Do not use any auxiliary data structures to solve this problem (no array, vector, stack, queue, string, etc).

Write the member function as it would appear in BinaryTree.cpp. You do not need to declare the function header that would appear in BinaryTree.h. Assume that you are adding this method to the BinaryTree class as defined below:

class BinaryTree {
    BinaryTreeNode* root;   // nullptr for an empty tree
    your code goes here;

struct BinaryTreeNode {
    int data;
    BinaryTreeNode* left;
    BinaryTreeNode* right;
Type your C++ solution code here:

This is a member function problem. Submit a member function that will become part of an existing C++ class. You do not need to write the complete class, just the member function described in the problem.

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