Size of a binary tree

Abhishek Kumar • Category: Data Structures • Tags: datastructures binary-tree

Find the size of a Binary tree using recursion or iterative solution. For example, a binary tree contains the following elements-
1, 2, 3, 4, 5, 6, 7
SIze of the binary tree will be 7.

To find the size of a binary tree we have to traverse each node one by one and count the nodes as long as we are getting nodes in the tree. Same logic can be applied to other trees like the Binary search tree.

We can solve this problem in two ways-

Recursive solution
Iterative solution

Recursive solution

For recursive solution we have to check each node one by one recursively as we have done in binary tree recursive traversal. Other types of traversal can also be used.

Python
Javascript

class Node:
    def __init__(self, data):
        self.left = None
        self.data = data
        self.right = None

def find_size(root):
    if root is None:
        return 0
    return find_size(root.left) + find_size(root.right) + 1

root = Node(1)
root.left = Node(2)
root.right = Node(3)
root.left.left = Node(4)
root.left.right = Node(5)
root.right.left = Node(6)
root.right.right = Node(7)
print(find_size(root))

class Node {
  constructor(data) {
    this.left = null;
    this.data = data;
    this.right = null;
  }
}

function findSize(root) {
  if (!root) return 0;
  return findSize(root.left) + findSize(root.right) + 1;
}

const root = new Node(1);
root.left = new Node(2);
root.right = new Node(3);
root.left.left = new Node(4);
root.left.right = new Node(5);
root.right.left = new Node(6);
root.right.right = new Node(7);
console.log(findSize(root));

Output

Iterative solution

For iterative solution, we have to traverse each node in level order and count each node one by one.

Python
Javascript

import queue

class Node:
    def __init__(self, data):
        self.left = None
        self.data = data
        self.right = None

def find_size(root):
    if root is None:
        return 0
        
    q = queue.Queue()
    q.put(root)
    count = 0
    while not q.empty():
        count = count + 1
        node = q.get()
        if node.left:
            q.put(node.left)
        if node.right:
            q.put(node.right)
    return count

root = Node(1)
root.left = Node(2)
root.right = Node(3)
root.left.left = Node(4)
root.left.right = Node(5)
root.right.left = Node(6)
root.right.right = Node(7)
print(find_size(root))

class Node {
  constructor(data) {
    this.left = null;
    this.data = data;
    this.right = null;
  }
}

function findSize(root) {
  if (!root) return 0;

  const q = [];
  q.push(root);
  count = 0;

  while (q.length > 0) {
    count = count + 1;

    let node = q.shift();
    if (node.left) {
      q.push(node.left);
    }
    if (node.right) {
      q.push(node.right);
    }
  }
  return count;
}

const root = new Node(1);
root.left = new Node(2);
root.right = new Node(3);
root.left.left = new Node(4);
root.left.right = new Node(5);
root.right.left = new Node(6);
root.right.right = new Node(7);
console.log(findSize(root));