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

Write a member function named completeToLevel that could be added to the BinaryTree class. Your function should accept an integer K as a parameter and adds nodes with value -1 to a tree so that the first K levels are complete. A level is complete if every possible node at that level is non-NULL. We will use the convention that the overall root is at level 1, its children are at level 2, and so on. Preserve any existing nodes in the tree. For example, if a variable called tree refers to the tree below and you make the call of tree.completeToLevel(3);, you should fill in nodes to ensure that the first 3 levels are complete. Notice that level 4 of the tree below is not complete after the call. Keep in mind that you might need to fill in several different levels. Your function should throw an integer exception if passed a value for K that is less than 1.

tree after tree.completeToLevel(3);
     /  \
   83    6
  /       \
19         87
  \       /
   48   75
      /    \
   83        6
  /  \      / \
19   -1   -1   87
  \           /
   48       75

Constraints: 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;   // NULL 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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