Write a program to Calculate Size of a tree | Recursion

Difficulty Level : Easy
Last Updated : 02 Jul, 2021

Size of a tree is the number of elements present in the tree. Size of the below tree is 5.

Example Tree

Size() function recursively calculates the size of a tree. It works as follows:
Size of a tree = Size of left subtree + 1 + Size of right subtree.

Algorithm:

size(tree)
1. If tree is empty then return 0
2. Else
     (a) Get the size of left subtree recursively  i.e., call 
          size( tree->left-subtree)
     (a) Get the size of right subtree recursively  i.e., call 
          size( tree->right-subtree)
     (c) Calculate size of the tree as following:
            tree_size  =  size(left-subtree) + size(right-
                               subtree) + 1
     (d) Return tree_size

C++

// A recursive C++ program to
// calculate the size of the tree
#include <bits/stdc++.h>
using namespace std;
 
/* A binary tree node has data, pointer to left child
and a pointer to right child */
class node
{
    public:
    int data;
    node* left;
    node* right;
};
 
/* Helper function that allocates a new node with the
given data and NULL left and right pointers. */
node* newNode(int data)
{
    node* Node = new node();
    Node->data = data;
    Node->left = NULL;
    Node->right = NULL;
         
    return(Node);
}
 
/* Computes the number of nodes in a tree. */
int size(node* node)
{
    if (node == NULL)
        return 0;
    else
        return(size(node->left) + 1 + size(node->right));
}
 
/* Driver code*/
int main()
{
    node *root = newNode(1);
    root->left = newNode(2);
    root->right = newNode(3);
    root->left->left = newNode(4);
    root->left->right = newNode(5);
     
    cout << "Size of the tree is " << size(root);
    return 0;
}
 
// This code is contributed by rathbhupendra

C

#include <stdio.h>
#include <stdlib.h>
 
/* A binary tree node has data, pointer to left child
   and a pointer to right child */
struct node
{
    int data;
    struct node* left;
    struct node* right;
};
 
/* Helper function that allocates a new node with the
   given data and NULL left and right pointers. */
struct node* newNode(int data)
{
  struct node* node = (struct node*)
                       malloc(sizeof(struct node));
  node->data = data;
  node->left = NULL;
  node->right = NULL;
   
  return(node);
}
 
/* Computes the number of nodes in a tree. */
int size(struct node* node)
{ 
  if (node==NULL)
    return 0;
  else    
    return(size(node->left) + 1 + size(node->right)); 
}
 
/* Driver program to test size function*/   
int main()
{
  struct node *root = newNode(1);
  root->left        = newNode(2);
  root->right       = newNode(3);
  root->left->left  = newNode(4);
  root->left->right = newNode(5);  
 
  printf("Size of the tree is %d", size(root)); 
  getchar();
  return 0;
}

Java

// A recursive Java program to calculate the size of the tree
 
/* Class containing left and right child of current
   node and key value*/
class Node
{
    int data;
    Node left, right;
 
    public Node(int item)
    {
        data = item;
        left = right = null;
    }
}
 
/* Class to find size of Binary Tree */
class BinaryTree
{
    Node root;
 
    /* Given a binary tree. Print its nodes in level order
       using array for implementing queue */
    int size()
    {
        return size(root);
    }
 
    /* computes number of nodes in tree */
    int size(Node node)
    {
        if (node == null)
            return 0;
        else
            return(size(node.left) + 1 + size(node.right));
    }
 
    public static void main(String args[])
    {
        /* creating a binary tree and entering the nodes */
        BinaryTree tree = new BinaryTree();
        tree.root = new Node(1);
        tree.root.left = new Node(2);
        tree.root.right = new Node(3);
        tree.root.left.left = new Node(4);
        tree.root.left.right = new Node(5);
 
        System.out.println("The size of binary tree is : "
                            + tree.size());
    }
}

Python

# Python Program to find the size of binary tree
 
# A binary tree node
class Node:
 
    # Constructor to create a new node
    def __init__(self, data):
        self.data = data
        self.left = None
        self.right = None
 
# Computes the number of nodes in tree
def size(node):
    if node is None:
        return 0
    else:
        return (size(node.left)+ 1 + size(node.right))
 
 
# Driver program to test above function
root = Node(1)
root.left = Node(2)
root.right = Node(3)
root.left.left  = Node(4)
root.left.right = Node(5)
 
print "Size of the tree is %d" %(size(root))
 
# This code is contributed by Nikhil Kumar Singh(nickzuck_007)

C#

using System;
 
// A recursive C# program to calculate the size of the tree
 
/* Class containing left and right child of current
   node and key value*/
public class Node
{
    public int data;
    public Node left, right;
 
    public Node(int item)
    {
        data = item;
        left = right = null;
    }
}
 
/* Class to find size of Binary Tree */
public class BinaryTree
{
    public Node root;
 
    /* Given a binary tree. Print its nodes in level order
       using array for implementing queue */
    public virtual int size()
    {
        return size(root);
    }
 
    /* computes number of nodes in tree */
    public virtual int size(Node node)
    {
        if (node == null)
        {
            return 0;
        }
        else
        {
            return (size(node.left) + 1 + size(node.right));
        }
    }
 
    public static void Main(string[] args)
    {
        /* creating a binary tree and entering the nodes */
        BinaryTree tree = new BinaryTree();
        tree.root = new Node(1);
        tree.root.left = new Node(2);
        tree.root.right = new Node(3);
        tree.root.left.left = new Node(4);
        tree.root.left.right = new Node(5);
 
        Console.WriteLine("The size of binary tree is : " + tree.size());
    }
}
 
  //  This code is contributed by Shrikant13

Javascript

<script>
 
      // A recursive JavaScript program to
      // calculate the size of the tree
 
      /* Class containing left and right child of current
         node and key value*/
      class Node {
        constructor(item) {
          this.data = item;
          this.left = null;
          this.right = null;
        }
      }
 
      /* Class to find size of Binary Tree */
      class BinaryTree {
        constructor() {
          this.root = null;
        }
        /* computes number of nodes in tree */
        size(node = this.root) {
          if (node == null) {
            return 0;
          } else {
            return this.size(node.left) + 1 + this.size(node.right);
          }
        }
      }
      /* creating a binary tree and entering the nodes */
      var tree = new BinaryTree();
      tree.root = new Node(1);
      tree.root.left = new Node(2);
      tree.root.right = new Node(3);
      tree.root.left.left = new Node(4);
      tree.root.left.right = new Node(5);
 
      document.write("Size of the tree is " + tree.size() + "<br>");
       
</script>

Output:

Size of the tree is 5

Time & Space Complexities: Since this program is similar to traversal of tree, time and space complexities will be same as Tree traversal (Please see our Tree Traversal post for details)

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