Binary Search Tree Using Classes - c++

Question

I have been trying to implement binary search tree using classes. Every time I try to compile and run the program, the program ends. I have tried many things like making the *root public to access it in main so I can update the root, but somehow it becomes null every time.
Help will be appreciated.
This is for my university project.
#include <iostream>
using namespace std;
class tree;
class Node {
friend class tree;
private:
Node *lchild,*rchild;
int data;
public:
Node (int x) {
data = x;
lchild = rchild = NULL;
}
};
class tree {
protected:
Node* root;
void inorder(const Node* root)const;
public:
tree () {
root = NULL;
}
bool insert(int item);
void inorder() const {inorder(root);};
Node* getroot() {
return root;
}
};
bool tree :: insert(int item) {
if (root == NULL) {
Node *temp = new Node(item);
root = temp;
return (bool) root;
}
if (item < root -> data) {
insert(item);
}
if (item > root -> data) {
insert(item);
}
else if (item == root -> data) {
cout<<"Duplicate";
exit (0);
}
return (bool) root;
}
void tree :: inorder(const Node *root)const {
if (root != NULL) {
inorder(root -> lchild);
cout<<root -> data;
inorder(root -> rchild);
}
}
int main()
{
tree obj1;
obj1.insert(3);
//obj1.insert(4);
obj1.insert(1);
//obj1.insert(5);
obj1.inorder();
}

Answer 1

/* Program to implement Binary Search Tree in c++ using classes and objects */
#include<iostream>
#include<stdlib.h>
#include<cstdlib>
using namespace std;
struct Node {
int data;
Node* left;
Node* right;
};
class BinaryTree {
private:
struct Node* root;
public:
BinaryTree() {
root = NULL;
}
Node* createNode(int);
Node* insertNode(Node*, int);
Node* deleteNode(Node*, int);
void inOrder(Node*);
void preOrder(Node*);
void postOrder(Node*);
Node* findMinimum(Node*);
/* accessor function helps to
get the root node in main function
because root is private data member direct access is not possible */
Node* getRoot() {
return root;
}
/* mutator method helps to update root ptr after insertion
root is not directly updatable in the main because its private data member */
void setRoot(Node* ptr) {
root = ptr;
}
};
/* Helper function to create a new node in each function call of insertNode */
Node* BinaryTree :: createNode(int n) {
Node* newNode = new struct Node();
newNode->data = n;
newNode->left = NULL;
newNode->right = NULL;
return newNode;
}
/* Helps to get inorder predessor to delete the node from tree */
Node* BinaryTree :: findMinimum(Node* rootPtr) {
while(rootPtr->left != NULL) {
rootPtr = rootPtr->left;
}
return rootPtr;
}
/* insertion of the Node */
Node* BinaryTree :: insertNode(Node* rootPtr, int n) {
if(rootPtr == NULL) {
return createNode(n);
}
if(n < rootPtr->data) {
rootPtr->left = insertNode(rootPtr->left, n);
}
if(n > rootPtr->data) {
rootPtr->right = insertNode(rootPtr->right, n);
}
return rootPtr;
}
/* function to delete the Node */
Node* BinaryTree :: deleteNode(Node* rootPtr, int n) {
if(rootPtr == NULL) {
cout<<"Node to be deleted is not present.!"<<endl;
return rootPtr;
}
else if(n < rootPtr->data) {
rootPtr->left = deleteNode(rootPtr->left, n);
} else if(n > rootPtr->data) {
rootPtr->right = deleteNode(rootPtr->right, n);
} else {
if(rootPtr->left == NULL && rootPtr->right == NULL) {
delete rootPtr;
rootPtr = NULL;
}
else if(root->left == NULL) {
struct Node* temp = rootPtr;
rootPtr = rootPtr->right;
delete temp;
}
else if(rootPtr->right == NULL) {
struct Node* temp = rootPtr;
rootPtr = rootPtr->left;
delete temp;
} else {
Node* temp = findMinimum(rootPtr->right);
rootPtr->data = temp->data;
rootPtr->left = deleteNode(rootPtr->right, temp->data);
}
}
return rootPtr;
}
/* all traversal technique */
void BinaryTree :: inOrder(Node* root) {
if(root == NULL) {
return;
}
inOrder(root->left);
cout<<root->data<<"\t";
inOrder(root->right);
}
void BinaryTree :: preOrder(Node* root) {
if(root == NULL) return;
cout<<root->data<<"\t";
preOrder(root->left);
preOrder(root->right);
}
void BinaryTree :: postOrder(Node* root) {
if(root == NULL) return;
postOrder(root->left);
postOrder(root->right);
cout<<root->data<<"\t";
}
int main() {
BinaryTree l1;
int ch, ele, res;
Node* ptr;
do {
cout<<"1 - Insert Node\n";
cout<<"2 - IN-ORDER Traversal\n";
cout<<"3 - PRE-ORDER Traversal\n";
cout<<"4 - POST-ORDER Traversal\n";
cout<<"Enter choice\n";
cin>>ch;
switch(ch) {
case 1:
cout<<"Entre element to insert to the List\n";
cin>>ele;
/* calling insertNode function by passing root ptr to the function,
root ptr can be obtained by accessor function getRoot() */
ptr = l1.insertNode(l1.getRoot(), ele);
/* updating the root ptr*/
l1.setRoot(ptr);
break;
case 2:
cout<<"---IN-ORDER TRAVERSAL---"<<endl;
l1.inOrder(l1.getRoot());
cout<<endl;
break;
case 3:
cout<<"---PRE-ORDER TRAVERSAL---"<<endl;
l1.preOrder(l1.getRoot());
cout<<endl;
break;
case 4:
cout<<"---POST-ORDER TRAVERSAL---"<<endl;
l1.postOrder(l1.getRoot());
cout<<endl;
break;
case 5:
cout<<"Enter node to be deleted."<<endl;
cin>>ele;
ptr = l1.deleteNode(l1.getRoot(), ele);
l1.setRoot(ptr);
default: cout<<"Invalid choice"<<endl;
}
} while(ch >=1 && ch <= 5);
return 0;
}

Answer 2

The reason why root gets NULL again and again is that it actually never changes its value to something else than NULL.
Maybe you have introduced this behaviour in your code in the course of fixing some other issues; yet you assign root=NULL in the constructor; afterwards, you assign only obj.root1 = ..., while you return root in getroot() { return root; }. Further, you pass Node *root as parameter in you insert function; Note that this local variable named root hides data member root, such that root->... in these functions will always address the local variable and not the data member.
Before diving around in code that's interface needs a redesign, I'd suggest to adapt the design and then adapt the code; I'm pretty sure the errors will simply go away. I'd suggest to adapt the interface of class tree as follows and write the code around it.
Member function inorder() should be const to indicate that it does not alter the object's state. Note that const-member functions can - in contrast to other non-static member functions - be called on const-objects.
class Node {
friend class tree;
private:
Node *lchild,*rchild;
int data;
public:
Node (int x) {
data = x;
lchild = rchild = NULL;
}
};
class tree {
public:
tree () { root = NULL; }
bool insert(int item) { return insert(item,root); };
void inorder() const { inorder(root);};
protected:
Node* root;
void inorder(const Node* curr) const;
bool insert(int item, Node* curr);
};
bool tree :: insert(int item, Node *currNode) {
if (root == NULL) {
root = new Node(item);
return true;
}
else if (item < currNode->data) {
if (currNode->lchild == NULL) {
currNode->lchild = new Node(item);
return true;
}
else {
return insert(item, currNode->lchild);
}
}
else if (item > currNode->data) {
if (currNode->rchild == NULL) {
currNode->rchild = new Node(item);
return true;
}
else {
return insert(item, currNode->rchild);
}
}
else // item == currNode->data
return false; // duplicate; do not insert
}

Answer 3

The biggest problem with your code are the following lines:
if (item < root -> data) {
insert(item);
}
if (item > root -> data) {
insert(item);
}
Basically you are saying that if the item is larger or smaller than the root data you will call the function again with the same item, you never changed the item and you will basically do this an infinity amount of times.....