Find the Size of a Binary Tree without Recursion

Objective: Given a binary tree, Write an non-recursive algorithm to find the size of the tree.

Note : Size of the tree is num­ber of nodes in the tree

Size-of-Binary-Tree-exampleApproach:

In our earlier post (link) we have seen the clean and simple recursive approach for finding the size of the tree. Now we will see how to solve it without recursion.

If we are not using recursion then we need a data structure to store the tree traversal, we will use queue here.

Solution is exactly similar to tree traversal without recursion. Just that we will keep counting the number of nodes.

Code:

import java.util.LinkedList;
import java.util.Queue;
public class T_TreeSizeWithOutRecursion {
// If we are not using recursion then we need a data structure to store the
// tree traversal, we will use queue here
public static int getSize(Node root) {
if (root != null) {
int size=0; // size of tree
Queue<Node> q = new LinkedList<>();
// add root to the queue
q.add(root);
while (!q.isEmpty()) {
Node x = q.poll();
//increment the size
size++;
//add children to the queue
if(x.left!=null){
q.add(x.left);
}
if(x.right!=null){
q.add(x.right);
}
}
return size;
}
// if root is null, return 0
return 0;
}
public static void main(String[] args) {
Node 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);
System.out.println("Tree Size: " + getSize(root));
}
}
class Node {
int data;
Node left;
Node right;
public Node(int data) {
this.data = data;
}
}


Output:

Tree Size: 5