二叉树仅添加到根

Question

I'm writing a simple Binary Tree program in C++ and right now it only stores the most recent value entered at the root node eg. if I enter 10 into the tree then 9 into the tree, 9 just overwrites 10 as the root node so the tree only stores the value 9.

I've looked at multiple C++ Binary Tree solutions online and tried their version of implementing them yet I still get no success.

Here is my struct for a single node in the tree

struct TreeNode{

    int value;
    TreeNode *left;
    TreeNode *right;

    TreeNode(int value){

        this -> value = value;
        left = NULL;
        right = NULL;

    }
};

My class for the binary tree so far

class IntTree{

private :

    TreeNode *root;

public :

    IntTree();
    TreeNode* getRoot();
    void insertValue(TreeNode *root, int intValue);
    TreeNode* searchTree(TreeNode *root, int intValue);
    void inOrder(TreeNode *root);
    void deleteValue(int intValue);
    void deleteTree(TreeNode *root);

};

The Insert Method

void IntTree::insertValue(TreeNode *root, int intValue){


if(root == NULL){

    root = new TreeNode(intValue);

}

else if(intValue == root->value){

    cout << "Value already exists in the tree" << endl;

}

else if(intValue < root->value){

    insertValue(root->left, intValue);

}

else{

    insertValue(root->right, intValue);

}   
}

And then this method is simply called in a menu like this

cout << "Enter Value to Insert : " << endl;
input = readInt();
theTree.insertValue(theTree.getRoot(), input);

The logic all seems fine to me, apart from that I've tried not using a constructor and just induvidually setting the variable, having two functions for inserting one with just the int parameter which so I don't have to use the getRoot() later on and a million other things which I've forgotten

Answer 1

The answer is simple, the pointer you are modifying is only a copy, so the copy is discarded at the end of the function and you have lost memory. You need to take a reference on the pointer to actually modify it (nothing else to modify):

void insertValue(TreeNode *& root, int intValue)

Answer 2

This should work:

New insertvalue function call will look as below

void insertValue(TreeNode **root, int intValue)
{
  if(*root == NULL)
  {
      *root = newNode(intValue);
  }
  else if(intValue == (*root)->value)
  {
     cout << "Value already exists in the tree" << endl;
  }
  else if(intValue < (*root)->value)
  {
    insertValue(&(*(root))->left, intValue);
  }
  else
  {
    insertValue(&(*(root))->right, intValue);
  }   
}
int main()
{
    //initial code
    insertvalue(&root,value) //root is a single pointer variable.
    //code for printing the tree
}

There are many less complex ways to implement the same. i have just modified your code.