剑指offer系列33-----把二叉树打印成多行

【题目】从上到下按层打印二叉树，同一层结点从左至右输出。每一层输出一行。

方法一：直接打印

 package com.exe7.offer;

 import java.util.LinkedList;
 import java.util.Queue;

 /**
  * 【题目】从上到下按层打印二叉树，同一层结点从左至右输出。每一层输出一行。
  * @author WGS
  *
  */
 public class PrintBiTreeFromTopToBottom {
     static class TreeNode{
         int val=0;
         TreeNode left=null;
         TreeNode right=null;
         public TreeNode(int val){
             this.val=val;
         }
     }

     public void printBiTreeFromTopToBottom(TreeNode headNode){
         if(headNode==null) return ;
         int nextLevelNodes=0;
         int toBoPrint=1;//设置个初始值
         Queue<TreeNode> queue=new LinkedList<TreeNode>();
         queue.add(headNode);
         while(!queue.isEmpty()){
             //1 打印
             TreeNode curNode=queue.poll();
             System.out.print(curNode.val+"  ");

             //2 添加左右结点
             if(curNode.left!=null){
                 queue.add(curNode.left);
                 nextLevelNodes++;//下层要打印的结点数+1
             }
             if(curNode.right!=null){
                 queue.add(curNode.right);
                 nextLevelNodes++;//下层要打印的结点数+1
             }
             //左右结点添加完后即打印完本层一个结点值，自动减1（要判断本层是否还有别的值）
             --toBoPrint;
             if(toBoPrint==0){//本层打印完
                 System.out.println();//换行
                 toBoPrint=nextLevelNodes;//下层要打印的结点数
                 nextLevelNodes=0;//清0
             }
         }

     }
     public static void main(String[] args) {
         PrintBiTreeFromTopToBottom p=new PrintBiTreeFromTopToBottom();
          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);

             root.left = node1;
             root.right = node2;
             node1.left = node3;
             node1.right = node4;
             node2.left = node5;
             node2.right = node6;

            p.printBiTreeFromTopToBottom(root);
     }

 }

方法二：使用博主的方法（面试时候推荐此种方法，个别代码差异，思想一样）

 package com.exe7.offer;

 import java.util.ArrayList;
 import java.util.LinkedList;
 import java.util.Queue;

 /**方法二：使用博主的方法（面试时候推荐此种方法，个别代码差异，思想一样）
  * 【题目】从上到下按层打印二叉树，同一层结点从左至右输出。每一层输出一行。
  * @author WGS
  *
  */
 public class PrintBiTreeFromTopToBottom2 {
     static class TreeNode{
         int val=0;
         TreeNode left=null;
         TreeNode right=null;
         public TreeNode(int val){
             this.val=val;
         }
     }

     public ArrayList<ArrayList<Integer>> printBiTreeFromTopToBottom(TreeNode headNode){
         ArrayList<ArrayList<Integer>> list=new ArrayList<>();//接收总共行的结点
         ArrayList<Integer> nodeList=new ArrayList<>();//接收每行结点
         if(headNode==null) return list;
         int nextLevelNodes=0;//下层要打印的结点数
         int toBoPrint=1;//设置个初始值
         Queue<TreeNode> queue=new LinkedList<TreeNode>();
         queue.add(headNode);
         while(!queue.isEmpty()){
             //1 打印
             TreeNode curNode=queue.poll();
             //System.out.print(curNode.val+"  ");
             nodeList.add(curNode.val);
             //2 添加左右结点
             if(curNode.left!=null){
                 queue.add(curNode.left);
                 nextLevelNodes++;//下层要打印的结点数+1
             }
             if(curNode.right!=null){
                 queue.add(curNode.right);
                 nextLevelNodes++;//下层要打印的结点数+1
             }
             //左右结点添加完后即打印完本层一个结点值，自动减1（要判断本层是否还有别的值）
             --toBoPrint;
             if(toBoPrint==0){//本层打印完
                 //System.out.println();//换行
                 list.add(nodeList);
                 toBoPrint=nextLevelNodes;//下层要打印的结点数
                 nextLevelNodes=0;//清0
                 nodeList=new ArrayList<>();
             }
         }
         return list;

     }
     public static void main(String[] args) {
         PrintBiTreeFromTopToBottom2 p=new PrintBiTreeFromTopToBottom2();
          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);

             root.left = node1;
             root.right = node2;
             node1.left = node3;
             node1.right = node4;
             node2.left = node5;
             node2.right = node6;

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

 }