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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;
}

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