关于二叉树的按层打印

本文的思路来自于牛客网左程云大大的二叉树视频

视频地址

​​http://www.nowcoder.com/courses/1/1/1​​

题目要求如下:

至于算法分析,大家看视频吧,左老大讲的肯定比我清楚,下面是我实现的代码

class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;
    }

}


public class Solution {
    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);
        TreeNode t6=new TreeNode(6);
        TreeNode t7=new TreeNode(7);
        TreeNode t8=new TreeNode(8);
        
        t1.left=t2;  t1.right=t3;
        t2.left=t4;  t3.left=t5; t3.right=t6;
        t5.left=t7;  t5.right=t8;
        new Solution().printFromTopToBottom(t1);
        
    }


    public ArrayList<Integer> printFromTopToBottom(TreeNode root) {
        ArrayList<Integer> list=new ArrayList<Integer>();
        Queue <TreeNode> queue=new ArrayBlockingQueue<>(100);
        TreeNode last=root;     //当前行的最后节点
        TreeNode nLast=root;    //下一行的最右节点
        queue.add(root);
        
        
        while (!queue.isEmpty()) {
            TreeNode out=queue.poll();
            System.out.print(out.val+" "); 
            list.add(out.val);
            if (out.left!=null) {
                queue.add(out.left);
                nLast=out.left;
            }
            if (out.right!=null) {
                queue.add(out.right);
                nLast=out.right;
            }
            if (out==last) {
                System.out.println("");
                last=nLast;
            }
            
        }
        return list;
    }
}