Generic Iterative Depth-First Binary Tree Traversal with Stack in Java

A binary tree is a tree data structure in which each node has at most two children, which are referred to as the left child and the right child.

Depth-first search (DFS) is an algorithm for traversing or searching tree or graph data structures. One starts at the root(selecting some arbitrary node as the root in the case of a graph) and explores as far as possible along each branch before backtracking.

DFS requires the use of a data structure called Stack, which is a Last In First Out (LIFO) structure.

                                       Depth-First Traversal Sequence: 1 - 2 - 4 - 5 - 3 - 6

package interviewquestions;

import java.util.Stack;

class Node<T>
{
   private T data;
   private Node<T> left;
   private Node<T> right;
 
   Node( T pData, Node<T> pLeft, Node<T> pRight )
   {
     data = pData;
     left = pLeft;
     right = pRight;
   }
 
   public void setLeftChild( Node<T> pLeft ) {  left = pLeft; }  
   public void setRightChild( Node<T> pRight ) { right = pRight; } 
 
   public Node<T> getLeftChild() { return left; }
   public Node<T> getRightChild() { return right; }  
   public T getData() { return data; }

}

class BinaryTree<T>
{
   Node<T> root;
 
   public BinaryTree(){  root = null; } 
 
   public void setRootNode( Node<T> pRoot ) {  root = pRoot; }
 
   public void depthFirst()
   {
     depthFirst( root );   
   }
 
   private void depthFirst( Node<T> pNode )
   {
     if( pNode == null )
       return;   

     Stack<Node<T>> stack = new Stack<Node<T>>();
     stack.add(pNode);

     while (!stack.isEmpty()) {
         Node<T> node = stack.pop();

         if (node.getRightChild() != null)
             stack.add(node.getRightChild());
         if (node.getLeftChild() != null)
             stack.add(node.getLeftChild());
         System.out.print(node.getData());
     }

   }
  
}

public class DepthFirstTraversal {
 
 public static void main(String[] args) {
  
    Node<Integer> node1 = new Node<Integer>( 1, null, null );
    Node<Integer> node2 = new Node<Integer>( 2, null, null );
    Node<Integer> node3 = new Node<Integer>( 3, null, null );
    Node<Integer> node4 = new Node<Integer>( 4, null, null );
    Node<Integer> node5 = new Node<Integer>( 5, null, null );
    Node<Integer> node6 = new Node<Integer>( 6, null, null );
  
    node1.setLeftChild(node2);
    node1.setRightChild(node3);
  
    node2.setLeftChild(node4);
    node2.setRightChild(node5);
  
    node3.setRightChild(node6);
  
    BinaryTree<Integer> binaryTree = new BinaryTree<Integer>();
    binaryTree.setRootNode(node1);
  
    binaryTree.depthFirst();  
 }

}

Create a DepthFirstTraversal.java file in your workspace.

When the main method inside the DepthFirstTraversal class executed it is going to print :

1
2
4
5
3
6