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);
            }
    }

}