Algorithm for Postorder Tree Traversals : Iterative Model(Non-Recursive way)

import java.util.Stack; //Postorder Tree Traversals : Iterative Model(Non-Recursive way) class BinaryTreePostOrderTraversalIterativeModel {      class TreeNode {             TreeNode left, right;             int data; // considering integer data.                    public TreeNode(int dataItem) {                   this.data = dataItem;                   left = null;                   right = null;             }      }              TreeNode root;        BinaryTreePostOrderTraversalIterativeModel() {              root = null;        }               void printPostOrderTraversal(TreeNode treeNode) {              if(treeNode == null)                     return;                           //Left, Right, Data              Stack<TreeNode> s = new Stack<TreeNode>();              s.push(root);              while (!s.isEmpty()) {                     TreeNode current = s.peek();                     if ( current.left == null || current.right == null) {                           TreeNode node = s.pop();                           System.out.println(node.data);                     } else {                           if(current.right != null){                                  s.push(current.right);                                  current.right = null;                           }                           if(current.left != null){                                  s.push(current.left);                                  current.left = null;                           }                     }              }        }               void printPostOrder() {              printPostOrderTraversal(root);        }        public static void main(String[] args) {              BinaryTreePostOrderTraversalIterativeModel tree = new BinaryTreePostOrderTraversalIterativeModel();         tree.root = new TreeNode(1);                 tree.root.left = new TreeNode(2);         tree.root.right = new TreeNode(3);                 tree.root.left.left = new TreeNode(4);         tree.root.left.right = new TreeNode(5);                 tree.root.right.left = new TreeNode(6);         tree.root.right.right = new TreeNode(7);                 tree.printPostOrder();        } } //Time Complexity: O(n). Space Complexity: O(n).

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