Java: Get the Postorder traversal of its nodes' values of a given a binary tree

Last update on May 12 2025 13:11:13 (UTC/GMT +8 hours)

Postorder Binary Tree Traversal

Write a Java program to get the Postorder traversal of its nodes' values in a binary tree.

Sample Binary Tree

Postorder Traversal:

Sample Solution:

Java Code:

class Node
{
    int key;
    Node left, right;

    public Node(int item)
    {
        // Constructor to create a new Node with the given item
        key = item;
        left = right = null;
    }
}

class BinaryTree
{
  // Root of Binary Tree
    Node root;

    BinaryTree()
    {
        // Constructor to create an empty binary tree
        root = null;
    }

 void print_Postorder(Node node)
    {
        if (node == null)
            return;

        // Recursively print the left subtree in postorder
        print_Postorder(node.left);

        // Recursively print the right subtree in postorder
        print_Postorder(node.right);

        // Print the key of the current node
        System.out.print(node.key + " ");
    }

 void print_Postorder()  
	{   
	   // Wrapper method to start printing the tree in postorder
	   print_Postorder(root);  
	}
        public static void main(String[] args)
    {
       BinaryTree tree = new BinaryTree();

        // Create a binary tree with nodes and keys
        tree.root = new Node(55);
        tree.root.left = new Node(21);
        tree.root.right = new Node(80);
        tree.root.left.left = new Node(9);
        tree.root.left.right = new Node(29);
        tree.root.right.left = new Node(76);
        tree.root.right.right = new Node(91);

        // Display a message and initiate the postorder traversal
        System.out.println("\nPostorder traversal of binary tree is: ");
        tree.print_Postorder();
    }
}

Sample Output:

Postorder traversal of binary tree is: 
9 29 21 76 91 80 55  

Flowchart:

For more Practice: Solve these Related Problems:

• Modify the program to return postorder traversal as a list.
• Write a program to perform a non-recursive postorder traversal.
• Modify the program to print postorder traversal using a single stack.
• Write a program to perform a postorder traversal on a binary search tree.

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