剑指Offer：二叉树打印成多行【23】

题目描述

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。

题目分析 

　　

Java题解

package tree;import java.util.ArrayList;import java.util.LinkedList;import java.util.Queue;public class PrintByLevel {    public static void main(String[] args) {        TreeNode t1 = new TreeNode(1);        TreeNode t2 = new TreeNode(2);        TreeNode t3 = new TreeNode(3);        TreeNode t4 = new TreeNode(4);        TreeNode t5 = new TreeNode(5);        t1.left=t2;        t1.right=t3;        t2.left=t4;        t2.right=t5;    }    static ArrayList
     
      
       > Print(TreeNode pRoot) {        ArrayList
       
        
         > re = new ArrayList<>();        if (pRoot==null)            return re;        Queue
         
           queue = new LinkedList<>();        queue.add(pRoot);        int nextLevel =0;        int toBePrinted = 1;        ArrayList
          
            cuLevel = new ArrayList<>(); while (!queue.isEmpty()) { TreeNode tmp = queue.poll(); cuLevel.add(tmp.val); if(tmp.left!=null) { queue.add(tmp.left); nextLevel++; } if(tmp.right!=null) { queue.add(tmp.right); nextLevel++; } toBePrinted--; if(toBePrinted==0) { re.add(cuLevel); cuLevel = new ArrayList<>(); toBePrinted = nextLevel; nextLevel=0; } } return re; }}