//    题目描述//    请实现一个函数按照之字形打印二叉树，//    即第一行按照从左到右的顺序打印，//    第二层按照从右至左的顺序打印，//    第三行按照从左到右的顺序打印，//    其他行以此类推。    public class TreeNode {        int val = 0;        TreeNode left = null;        TreeNode right = null;        public TreeNode(int val) {            this.val = val;        }    }    public ArrayList
     
      
       > Print(TreeNode pRoot) {        ArrayList
       
        
         > arrayLists = new ArrayList
         
          
           >(); if (pRoot==null){ return arrayLists; } Stack
           
             stack1 = new Stack
            
             (); Stack
             
               stack2 = new Stack
              
               (); stack1.add(pRoot); while (!stack1.isEmpty() || !stack2.isEmpty()) { if (!stack1.isEmpty()) { ArrayList
               
                 arrayList = new ArrayList
                
                 (); while (!stack1.isEmpty()) { TreeNode node = stack1.pop(); arrayList.add(node.val); if (node.left != null) { stack2.add(node.left); } if (node.right != null) { stack2.add(node.right); } } arrayLists.add(arrayList); }else if (!stack2.isEmpty()) { ArrayList
                 
                   arrayList = new ArrayList
                  
                   (); while (!stack2.isEmpty()) { TreeNode node = stack2.pop(); arrayList.add(node.val); if (node.right != null) { stack1.add(node.right); } if (node.left != null) { stack1.add(node.left); } } arrayLists.add(arrayList); } } return arrayLists; }