Print a binary tree in zig zag level order

PrintZigZagOrder.java

/*
 * Print a binary tree in zig zag level order
 */

package Chapter4;

import java.util.Stack;

public class PrintZigZagOrder {
    public static void main(String args[]){
        TreeNode n1 = new TreeNode(1, null, null);
        TreeNode n2 = new TreeNode(2, n1, null);
        TreeNode n4 = new TreeNode(4, null, null);
        TreeNode n6 = new TreeNode(6, null, null);
        TreeNode n5 = new TreeNode(5, n4, n6);
        TreeNode n3 = new TreeNode(3, n2, n5);
        TreeNode n10 = new TreeNode(10, null, null);
        TreeNode n11 = new TreeNode(11, n10, null);
        TreeNode n9 = new TreeNode(9, null, n11);
        TreeNode n8 = new TreeNode(8, null, n9);
        TreeNode n7 = new TreeNode(7, n3, n8);
        
        printZigZagOrder(n7);
    }
    
    public static void printZigZagOrder(TreeNode root){
        Stack<TreeNode> s1 = new Stack<TreeNode>();
        Stack<TreeNode> s2 = new Stack<TreeNode>();
        Stack<TreeNode> tmp;
        s1.add(root);
        boolean leftToRight = false;
        while(!s1.isEmpty()){
            TreeNode n = s1.pop();
            System.out.print(n.data + " ");
           
            
            if(!leftToRight){
                if(n.left != null){
                    s2.push(n.left);
                }
                if(n.right != null){
                    s2.push(n.right);
                }
            }else{
                if(n.right != null){
                    s2.push(n.right);
                }
                if(n.left != null){
                    s2.push(n.left);
                }
            }
       
            if(s1.isEmpty()){
                leftToRight = !leftToRight;
                System.out.println();
                tmp = s1;
                s1 = s2;
                s2 = tmp;
            }
        }
    }
}