剑指offer系列34----按之字形顺序打印二叉树

【题目】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。

未优化，不是最优解，博主用的是队列，我用的栈。

方法一：直接打印

 package com.exe7.offer;

 import java.util.Stack;

 import org.junit.Test;

 /**方法一：直接打印
  * 【题目】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。
  * @author WGS
  *
  */
 public class PrintBiTree {
     static class TreeNode{
         int val=0;
         TreeNode left=null;
         TreeNode right=null;
         public TreeNode(int val){
             this.val=val;
         }
     }

     public void printZhiTree(TreeNode pRoot){
         if(pRoot==null) return;
         Stack<TreeNode> stack1=new Stack<>();
         Stack<TreeNode> stack2=new Stack<>();
         stack1.push(pRoot);
         int toBePrint=1;
         int nextLevelNodes=0;
         int level=1;
         TreeNode tempNode=null;

         while(!stack1.isEmpty() || !stack2.isEmpty()){
             if(level%2!=0){
                 tempNode=stack1.pop();
                 System.out.print(tempNode.val+" ");
                 --toBePrint;
                 if(tempNode.left!=null){
                     stack2.push(tempNode.left);
                     ++nextLevelNodes;
                 }
                 if(tempNode.right!=null){
                     stack2.push(tempNode.right);
                     ++nextLevelNodes;
                 }
             }else{
                 tempNode=stack2.pop();
                 System.out.print(tempNode.val+" ");
                 --toBePrint;

                 if(tempNode.right!=null){
                     stack1.push(tempNode.right);
                     ++nextLevelNodes;
                 }
                 if(tempNode.left!=null){
                     stack1.push(tempNode.left);
                     ++nextLevelNodes;
                 }
             }
             //
             if(toBePrint==0){
                 System.out.println("------------------");
                 level++;
                 toBePrint=nextLevelNodes;
                 nextLevelNodes=0;
             }
         }

     }

     //测试类
         public static void main(String[] args){
             PrintBiTree p=new PrintBiTree();
              TreeNode root = new TreeNode(8);
                 TreeNode node1 = new TreeNode(6);
                 TreeNode node2 = new TreeNode(10);
                 TreeNode node3 = new TreeNode(5);
                 TreeNode node4 = new TreeNode(7);
                 TreeNode node5 = new TreeNode(9);
                 TreeNode node6 = new TreeNode(11);
                 TreeNode node7 = new TreeNode(12);
                 TreeNode node8 = new TreeNode(13);
                 TreeNode node9 = new TreeNode(14);
                 TreeNode node10 = new TreeNode(15);
                 TreeNode node11 = new TreeNode(16);
                 TreeNode node12 = new TreeNode(17);
                 TreeNode node13 = new TreeNode(18);
                 TreeNode node14 = new TreeNode(19);

                 root.left = node1;
                 root.right = node2;
                 node1.left = node3;
                 node1.right = node4;
                 node2.left = node5;
                 node2.right = node6;
                 node3.left=node7;
                 node3.right=node8;
                 node4.left=node9;
                 node4.right=node10;
                 node5.left=node11;
                 node5.right=node12;
                 node6.left=node13;
                 node6.right=node14;

                 p.printZhiTree(root);
         }

 }

方法二：面试需要

 package com.exe7.offer;

 import java.util.ArrayList;
 import java.util.Stack;

 /**方法二：面试时候需要
  * 【题目】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。
  * @author WGS
  *
  */
 public class PrintBiTree2 {
     static class TreeNode{
         int val=0;
         TreeNode left=null;
         TreeNode right=null;
         public TreeNode(int val){
             this.val=val;
         }
     }

     public ArrayList<ArrayList<Integer>>  printZhiTree(TreeNode pRoot){
         ArrayList<ArrayList<Integer>> list=new ArrayList<>();
         if(pRoot==null) return list;
         ArrayList<Integer> nodeList=new ArrayList<Integer>();
         Stack<TreeNode> stack1=new Stack<>();
         Stack<TreeNode> stack2=new Stack<>();
         stack1.push(pRoot);
         int toBePrint=1;
         int nextLevelNodes=0;
         int level=1;
         TreeNode tempNode=null;

         while(!stack1.isEmpty() || !stack2.isEmpty()){
             if(level%2!=0){//奇数层
                 tempNode=stack1.pop();
                 //System.out.print(tempNode.val+" ");
                 nodeList.add(tempNode.val);
                 --toBePrint;
                 if(tempNode.left!=null){
                     stack2.push(tempNode.left);
                     ++nextLevelNodes;
                 }
                 if(tempNode.right!=null){
                     stack2.push(tempNode.right);
                     ++nextLevelNodes;
                 }

             }else{
                 tempNode=stack2.pop();
                 //System.out.print(tempNode.val+" ");
                 nodeList.add(tempNode.val);
                 --toBePrint;

                 if(tempNode.right!=null){
                     stack1.push(tempNode.right);
                     ++nextLevelNodes;
                 }
                 if(tempNode.left!=null){
                     stack1.push(tempNode.left);
                     ++nextLevelNodes;
                 }
             /*    if(toBePrint==0){
                     System.out.println();
                     list.add(nodeList);
                     level++;
                     toBePrint=nextLevelNodes;
                     nextLevelNodes=0;
                     nodeList=new ArrayList<Integer>();
                 }*/
             }
             if(toBePrint==0){
                 System.out.println();
                 list.add(nodeList);
                 level++;
                 toBePrint=nextLevelNodes;
                 nextLevelNodes=0;
                 nodeList=new ArrayList<Integer>();
             }
         }
         return list;

     }

     //测试类
         public static void main(String[] args){
             PrintBiTree2 p=new PrintBiTree2();
              TreeNode root = new TreeNode(8);
                 TreeNode node1 = new TreeNode(6);
                 TreeNode node2 = new TreeNode(10);
                 TreeNode node3 = new TreeNode(5);
                 TreeNode node4 = new TreeNode(7);
                 TreeNode node5 = new TreeNode(9);
                 TreeNode node6 = new TreeNode(11);
                 TreeNode node7 = new TreeNode(12);
                 TreeNode node8 = new TreeNode(13);
                 TreeNode node9 = new TreeNode(14);
                 TreeNode node10 = new TreeNode(15);
                 TreeNode node11 = new TreeNode(16);
                 TreeNode node12 = new TreeNode(17);
                 TreeNode node13 = new TreeNode(18);
                 TreeNode node14 = new TreeNode(19);

                 root.left = node1;
                 root.right = node2;
                 node1.left = node3;
                 node1.right = node4;
                 node2.left = node5;
                 node2.right = node6;
                 node3.left=node7;
                 node3.right=node8;
                 node4.left=node9;
                 node4.right=node10;
                 node5.left=node11;
                 node5.right=node12;
                 node6.left=node13;
                 node6.right=node14;

                 ArrayList<ArrayList<Integer>> getList=p.printZhiTree(root);;
                 for(ArrayList<Integer> a:getList){
                     System.out.println(a);
                 }

         }

 }