查找二叉树的父节点函数

Question

is it possible to write a function to return the parent node of a given node for a binary tree?

BinaryTree *search_val(BinaryTree *bt, int val)
{
    //temp pointer 
    BinaryTree* temp = NULL;
    if(!bt->isEmpty())
    {
        //check if root is equal to value and return root if true
        if(bt->getData() == val)
        {
            return bt;
        }
        else
        {
            //search left side
            temp = search_val(bt->left(), val);
            //if not found in left, search right
            if (temp == NULL)
            {
                temp = search_val(bt->right(), val);
            }
            return temp;
        }
        return NULL;
    }
    return NULL;
 }

I just have this search function at the moment. I got it from here actually. So I'm trying to convert this to search for the parent of a node. The parameters will be the root node and the node whose parent we want. Is that even possible? I just need some hints to get started then I'll post my code. The purpose of creating this function is because I have a delete leaf node function that works almost perfectly....the only problem is that when I print all nodes after deleting, the supposedly deleted node still appears. I'm sure it's because the parent node is still linked to it in main. Here's my delete leaf node function:

void delete_leaf_node(BinaryTree *bt, int val)
{
    BinaryTree *temp;
    temp = search_val(bt, val);
    //If node does not exist in the tree, inform the user
    if(temp == NULL)
    {
        cout << "\n   " << val << " was not found in the tree" << endl; 
    }
    //Check if node is a leaf
    else if(temp->isLeaf())
    {
        delete temp;
        cout << "\n   Leaf " << temp->getData() << " deleted" << endl;
    }
    //Inform user that node is not a leaf
    else 
        cout << "\n   " << temp->getData() << " is not a Leaf" << endl; 
    //Display using In Order Traversal to see that the node was actually deleted    
    cout << "\n   In Order Traversal after deleting: " << endl << "\n   ";
    inOrderTraverse(bt);
    cout << endl;
} 

I hope I'm making sense to someone...sorry I tried to shorten the question but couldn't.

BinaryTree.h file:

using namespace std;

//BinaryTree class
class BinaryTree{
    public:
        BinaryTree();
        bool isEmpty();
        bool isLeaf();
        int getData();
        void insert(const int &DATA);
        BinaryTree *left();
        BinaryTree *right();
        void makeLeft(BinaryTree *bt);
        void makeRight(BinaryTree *bt);
    private:
        bool nullTree;
        int treeData;
        BinaryTree *leftTree;
        BinaryTree *rightTree;
};

BinaryTree.cpp file:

#include <iostream>
#include "BinaryTree.h"

using namespace std;

//constructor
BinaryTree::BinaryTree()
{
    nullTree = true;
    leftTree = NULL;
    rightTree = NULL;
}

/*
  is_empty function for BinaryTree class. Does not take any parameters. 
  Returns true if tree is empty and false otherwise.
*/
bool BinaryTree::isEmpty()
{
    return nullTree;
}

/*
  is_leaf function for BinaryTree class. Does not take any parameters. 
  Returns true if node has no children and false otherwise.
*/
bool BinaryTree::isLeaf()
{
    return ((this->leftTree->treeData == 0) && (this->rightTree->treeData == 0));
}

/*
  getData function for BinaryTree class. Does not take any parameters. 
  Returns treeData value.
*/
int BinaryTree::getData()
{
    if(!isEmpty());
    return treeData;
}

/*
  insert function for BinaryTree class. Takes one parameter, passed by
  reference. Returns true if node has no children and false otherwise.
*/
void BinaryTree::insert(const int &DATA)
{
    //create empty children and insert DATA
    treeData = DATA;
    if(nullTree) 
    {
        nullTree = false;
        leftTree = new BinaryTree;
        rightTree = new BinaryTree;
    }
}

/*
  left function for BinaryTree class. It points to the left node.
  Does not take any parameters. Returns left node.
*/
BinaryTree *BinaryTree::left()
{
    if(!isEmpty());
    return leftTree;
}

/*
  right function for BinaryTree class. It points to the right node.
  Does not take any parameters. Returns right node.
*/
BinaryTree *BinaryTree::right()
{
    if(!isEmpty());
    return rightTree;
}

/*
  makeLeft function for BinaryTree class. Takes a pointer to a tree node as a parameter. 
  makes the parameter the left child of a node. Does not return any value
*/
void BinaryTree::makeLeft(BinaryTree *bt)
{
    if(!isEmpty());
    leftTree = bt;
}

/*
  makeRight function for BinaryTree class. Takes a pointer to a tree node as a parameter. 
  makes the parameter the right child of a node. Does not return any value
*/
void BinaryTree::makeRight(BinaryTree *bt)
{
    if (!isEmpty());
    rightTree = bt;
}

Thanks

Answer 1

That depends on your BinaryTree implementation. As far as I see, if you don't save a reference inside each node to his parent, you can't directly access to it when deleting

Edit

You can modify your BinaryTree class with:

class BinaryTree{
    public:
        BinaryTree();
        bool isEmpty();
        bool isLeaf();
        int getData();
        void insert(const int &DATA);
        BinaryTree *left();
        BinaryTree *right();
        void makeLeft(BinaryTree *bt);
        void makeRight(BinaryTree *bt);

        void setParent(BinaryTree *parent);
        BinaryTree* getParent();
    private:
        bool nullTree;
        int treeData;
        BinaryTree *leftTree;
        BinaryTree *rightTree;

        BinaryTree* parent;
};

Then in your .cpp :

BinaryTree::BinaryTree()
{
    nullTree = true;
    leftTree = NULL;
    rightTree = NULL;
    parent = NULL;
}

void BinaryTree::setParent(BinaryTree *parent){
    this->parent = parent;
}

BinaryTree* BinaryTree::getParent(){
    return parent;
}

Your delete function will look like:

void delete_leaf_node(BinaryTree *bt, int val)
{
    BinaryTree *temp;
    temp = search_val(bt, val);
    //If node does not exist in the tree, inform the user
    if(temp == NULL)
    {
        cout << "\n   " << val << " was not found in the tree" << endl; 
    }
    //Check if node is a leaf
    else if(temp->isLeaf())
    {
        // You must distinguish which child you are
        BinaryTree* parent = temp->getParent();
        BinaryTree* leftChild = parent->left;
        BinaryTree* rightChild = parent->right;
        if(leftChild == temp){
            parent->left = null;
        }
        if(rightChild == temp){
            parent->right = null;
        }
        delete temp;
        cout << "\n   Leaf " << temp->getData() << " deleted" << endl;
    }
    //Inform user that node is not a leaf
    else 
        cout << "\n   " << temp->getData() << " is not a Leaf" << endl; 
    //Display using In Order Traversal to see that the node was actually deleted    
    cout << "\n   In Order Traversal after deleting: " << endl << "\n   ";
    inOrderTraverse(bt);
    cout << endl;
}