This tutorial provides code for implementing post-order traversal of a Binary Tree.

Post-Order Traversal of Binary Tree

Binary Tree traversal is a process of visiting each node of Binary Tree exactly once. Post-Order traversal falls into depth-first search as search is deepended on child nodes of a node before moving to its sibling.

Post-order traversal is a special type of Tree traversal wherein left child and right child are visited before a node. This results into recursive function calls as you can't print a node data unless all of its left and right child nodes data have been printed.

Let's consider below Binary Tree - 

Here is the Post-Order Traversal of above tree -

20 10 40 30 60 90 80 70 50 

Java Implementation of Post-Order Traversal of Binary Tree

Here is Java code for Binary Tree containing methods for inserting data and post-order traversal - 

package com.aksain.data.structures;

public class BinaryTreeWithPostOrderTraversal<T extends Comparable<T>> {
	private Node root;
	
	private class Node {
		T data;
		Node left;
		Node right;
		
		private Node(T data) {
			this.data = data;
		}
	}
	
	private Node doInsert(T data, Node node) {
		if(node == null) {
			return new Node(data);
		}
		int result = data.compareTo(node.data);
		if(result < 0) {
			node.left = doInsert(data, node.left);
		} else if(result > 0) {
			node.right = doInsert(data, node.right);
		}
		
		return node;
	}
	
	public void insert(T data) {		
		root = doInsert(data, root);
	}
	
	private void doPostOrder(Node node) {
		if(node == null) {
			return;
		}
		doPostOrder(node.left);
		doPostOrder(node.right);
		System.out.print(node.data + " ");
	}
	
	public void postOrder() {
		doPostOrder(root);
		System.out.println();
	}
	
	public static void main(String[] args) {
		final BinaryTreeWithPostOrderTraversal<Integer> binaryTree = new BinaryTreeWithPostOrderTraversal<>();
		binaryTree.insert(50);
		binaryTree.insert(30);
		binaryTree.insert(10);
		binaryTree.insert(20);
		binaryTree.insert(40);
		binaryTree.insert(70);
		binaryTree.insert(60);
		binaryTree.insert(80);
		binaryTree.insert(90);
		
		binaryTree.postOrder();
	}
}

Here is the output of above code - 

20 10 40 30 60 90 80 70 50 

Thank you for reading through the tutorial. In case of any feedback/questions/concerns, you can communicate same to us through your comments and we shall get back to you as soon as possible.