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Language/Type: C++ binary trees pointers recursion
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Author: Marty Stepp (on 2016/08/27)

Write a function named tighten that accepts a reference to a pointer to the root of a binary tree of integers. Your function should eliminate branch nodes that have only one child. For example, if a variable named root points to the root of the tree below at left, the call of tighten(root); 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.

root after tighten(root);
(12 (28 (94 (65) (-8 / (10)))) (19 (32 / (72 (42) (50)))))
(12 (94 (65) (10)) (72 (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).

Assume that you are using the BinaryTreeNode structure as defined below:

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

This is a function problem. Write a C++ function as described. Do not write a complete program; just the function(s) above.

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