Skip to main content

Implementation of binary tree in C++


A binary tree is a non-linear data structure where every node has maximum two branches - left subtree and right subtree. An empty node is also a binary tree.

In earlier posts we have seen how to insert a node to binary tree, how to traverse a tree and how to delete nodes from tree.

The functions look almost similar in C++. Except that all these functions and root pointer are all parts of the class binary tree.

That is a good thing and a bad thing. If root is a data member (so private), how do we use root as a parameter in all the recursive functions - insert, delete, inorder etc?

Easy answer would be don't use recursion. Anyway no one like them.

So we can write insert and delete functions without using recursion and even search function. But traversal functions have to be recursive.

Ok, let us write a function to return root of the tree and use it as first parameter in all traversal functions.

Here is the complete class.

You can download this code along with test program from here


struct node
{
   int num;
   node *left;
   node *right;
};
class binarytree
{
   node *root;
public:
   binarytree();
   node* create_node(int val);
   void insert( int val); 
   void inorder(node *nd);
   void preorder(node *nd);
   void postorder(node *nd);
   node *search(node *nd,int val);
   void delete_node(int val);
   node*find_parent(node *nd);
   node*find_successor(node*nd,node**parent);
   node* get_root();
};
binarytree::binarytree()
{
    root = NULL;
}
node *binarytree::create_node(int val)
{
   node *newn = new node;
   newn->num = val;
   newn->left = NULL;
   newn->right = NULL;
   return newn;
}
void binarytree::insert( int val)
{//insert a node non-recursively
    node*newnode = create_node(val);
    if(root==NULL)
    {//tree is empty
       root = newnode;
       return;
    }
    node *temp = root;
    node *parent = NULL;
    while(temp!=NULL)
    {//find the location for new node
        parent = temp;
        if(temp->num >val)
           temp = temp->left;
        else
           temp = temp->right;
     }
     //which branch
     if(parent->num >val)
        parent->left = newnode;
     else
        parent->right = newnode;    
}

void binarytree::inorder(node *nd)
{
  if(nd!=NULL)
  {
     inorder(nd->left);
     cout<<nd->num<<"  ";
     inorder(nd->right);
   }
}
void binarytree::preorder(node *nd)
{
  if(nd!=NULL)
  {
     cout<<nd->num<<"  ";
     preorder(nd->left);   
     preorder(nd->right);
   }
}
void binarytree::postorder(node *nd)
{
  if(nd!=NULL)
  {
     postorder(nd->left);   
     postorder(nd->right);
     cout<<nd->num<<"  ";
   }
}
node* binarytree::search(node *nd, int val)
{
     if(nd==NULL)
       return nd;
     if(nd->num==val)
        return nd;
     if(nd->num > val)
       return search(nd->left,val);
     if(nd->num <val)
       return search(nd->right,val);
}
node *binarytree::find_parent(node *nd)
{
    if(nd==root)
    //root has no parent
       return NULL;
    node *temp = root;
    while(temp)
    {
       if(temp->left==nd || temp->right==nd)
          return temp;
       if(nd->num > temp->num)
         temp = temp->right;
       else if(nd->num <temp->num)
         temp = temp->left;
    }
    return NULL;
}
node*binarytree::find_successor(node*nd,node**parent)
{//successor is tree minimum of right subtree
   node*temp = nd->right;
   *parent = nd;
   while(temp->left!=NULL)
      {
      *parent=temp;
      temp = temp->left;
      }
   return temp;
}
         
void binarytree::delete_node(int val)
{
    node *dn = search(root,val);
    if(dn==NULL)
      {
        cout<<"value not found\n";
        return;
      }
     node*parent = find_parent(dn);
    if(dn->left!=NULL && dn->right!=NULL)
    {//node has both subtrees. delete successor instead
        node*successor = find_successor(dn,&parent);
        dn->num = successor->num;//copy data
        dn = successor;
    }    
   
    if(dn->left==NULL && dn->right==NULL)
    {//leaf node
       
        if(parent==NULL && dn==root)
           root = NULL;
        else if(parent==NULL)
           cout<<"Error";
        else
           if(dn==parent->left)
              parent->left = NULL;
           else if(dn==parent->right)
              parent->right = NULL;
        delete dn;
    }
    else if(dn->left==NULL||dn->right==NULL)
    {//has one child
         
         node* child = dn->left?dn->left:dn->right;
         if(dn==root)
             root = child;
         else{
            if(parent->left==dn)
              parent->left = child;
            else
             parent->right = child;
          }
          delete dn;
    }
}
node*binarytree::get_root()
{
   return root;
}
Labels:

Comments

Post a Comment

Popular posts from this blog

Linked list in C++

A linked list is a versatile data structure. In this structure, values are linked to one another with the help of addresses. I have written in an earlier post about how to create a linked list in C.  C++ has a library - standard template library which has list, stack, queue etc. data structures. But if you were to implement these data structures yourself in C++, how will you implement? If you just use new, delete, cout and cin, and then claim it is your c++ program, you are not conforming to OOPS concept. Remember you have to "keep it together". Keep all the functions and variables together - in a class. You have to have class called linked list in which there are methods - append, delete, display, insert, find, find_last. And there will also be a data - head. Defining node We need a structure for all these nodes. A struct can be used for this purpose, just like C. struct node { int val; struct node * next; }; Next we need to define our class. W
Post a Comment
Read more

Swap nodes of a linked list

Qn: Write a function to swap the adjacent nodes of a singly linked list.i.e. If the list has nodes as 1,2,3,4,5,6,7,8, after swapping, the list should be 2,1,4,3,6,5,8,7 Image from: https://tekmarathon.com Though the question looks simple enough, it is tricky because you don't just swap the pointers. You need to take care of links as well. So let us try to understand how to go about it. Take two adjacent nodes p1 and p2 Let prevnode be previous node of p1 Now link prevnode to p2 Link p2 to p1 Link p1 to next node of p2 So the code will be prevnode -> next = p2; p1 -> next = p2 -> next; p2 -> next = p1; But what about the start node or head? head node does not have previous node If we swap head with second node, modified head should be sent back to caller  To take care of swapping first and second nodes, we can write p1 = head; p2 = head -> next; p1 -> next = p2 -> next; p2 -> next = p1; head = p2;  Now we are read
Post a Comment
Read more

Binary tree deletion - non-recursive

In the previous post we have seen how to delete a node of a binary search tree using recursion. Today we will see how to delete a node of BST using a non-recursive function. Let us revisit the 3 scenarios here Deleting a node with no children just link the parent to NULL Deleting a node with one child link the parent to  non-null child of node to be deleted Deleting a node with both children select the successor of node to be deleted copy successor's value into this node delete the successor In order to start, we need a function to search for a node in binary search tree. Did you know that searching in  a BST is very fast, and is of the order O(logn). To search Start with root Repeat until value is found or node is NULL If the search value is greater than node branch to right If the search value is lesser than node branch to left.  Here is the function NODEPTR find_node (NODEPTR root,NODEPTR * parent, int delval) { NODEPTR nd = root; NODEPTR pa = root; if (root -> v
Post a Comment
Read more