How to Print Leaf Nodes of a Binary Tree in Java

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1. Introduction

In this post, we will see how to count leaf nodes in a binary tree in Java. Understanding how to count leaf nodes is useful for various applications in computer science, such as calculating the depth or height of a tree, optimizing search operations, and more. It is also a common interview question to practice questions on binary trees.

2. What are Leaf Nodes?

Leaf nodes are the nodes which don’t have any children. These are also terminal nodes and denote the end of the tree structure.

3. Implementation

There are two ways to count leaf nodes in a binary tree:

  • Recursive
  • Iterative

4.1 Recursive Solution

The recursive solution is very straightforward. Here are the steps for counting the number of leaf nodes:

The time complexity for the recursive approach is O(n), where n is the number of nodes in the binary tree. This is because each node in the tree is visited to determine whether it is a leaf node or not.

The space complexity of Level Order traversal is O(w) where w is the maximum width in the binary tree. This is because the maximum number of nodes in the queue is proportional to the width of the binary tree at any point in time.

4.2 Iterative Solution

For recursion, we use an implicit stack. So here, to convert the recursive solution to iterative, we will use an explicit stack.
Steps for the iterative solution:

  • Create an empty stack and push the root node to it.
  • Do the following when the stack is not empty:
    • Pop a node from the stack and check if it is a leaf node. If yes, print the node.
    • Push the right child of the popped node to the stack.
    • Push the left child of the popped node to the stack.

We are pushing the right child first, so it will be processed after the left subtree as the Stack is LIFO (Last In, First Out).

5. Complete Java Program

Let’s say our binary tree is:

Binary tree

Here is complete java program for printing leaf nodes:

Run above program and you will get following output:


6. Conclusion

In this article, we covered about how to print leaf nodes in Binary tree. We have discussed two approaches: Iterative and Recursive. We also discussed about time and space complexity for the same.
Java Binary tree tutorial:

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