层序遍历非队列方法

不使用队列，实现层序遍历

import static java.lang.Integer.max;

public class LayerOrderLearn {

    public static void main(String[] args) {
        int arr[]={1,2,3,4,5,6,7,8,9,10};
        BiTNode root = createTree1(arr, 0, arr.length - 1);
        //inOrder(root);
        //printThisLevel(root,4);
        LayerOrder(root);
    }

    //1、建树
    static BiTNode createTree1(int arr[],int start,int end){
        if(end-start<0) return null;

        int mid=(start+end+1)/2;
        BiTNode root = new BiTNode();
        root.data=arr[mid];
        root.left=createTree1(arr,start,mid-1);
        root.right=createTree1(arr,mid+1,end);

        return root;
    }

    //建树【方法二】
    static BiTNode createTree(int arr[],int start,int end){
        BiTNode root=null;
        if (start<=end){
            int mid=(start+end+1)/2;
            root=new BiTNode();
            root.data=arr[mid];
            root.left=createTree(arr,start,mid-1);
            root.right=createTree(arr,mid+1,end);
        }
        return root;
    }

    /*
    static int Height(BiTNode root){

        BiTNode temp=root;
        int height=0;
        while(temp!=null){
            height++;
            temp=temp.right;
        }
        return height;
    }*/

    //2、求树的高度
    static int TreeHeight(BiTNode root){
        if (root==null)return 0;
        return max(TreeHeight(root.left),TreeHeight(root.right))+1;
    }

    //3、打印树的指定层的结点
    static void printThisLevel(BiTNode root,int level){  //root出口，level出口

        if(root==null) return;

        if(level==1) System.out.print(root.data+" ");  //有可能是空节点了，但是level=1，这时打印就会出错了
        if(level<=0) return;
        //if(root==null) return;

        printThisLevel(root.left,level-1);
        printThisLevel(root.right,level-1);
    }

    //4、层序遍历
    static void LayerOrder(BiTNode root){
        int h=TreeHeight(root);
        for (int i = 1; i <=h ; i++) {
            printThisLevel(root,i);
        }
        /*while(h>=1){
            printThisLevel(root,h);
            h--;
        }*/
    }

    //[测试] 中序遍历
    public static void inOrder(BiTNode root){
        if (root==null)return;
        inOrder(root.left);
        System.out.print(root.data+" ");
        inOrder(root.right);
    }

    //*** 树的结点 ***
    static class  BiTNode{
        int data;
        BiTNode left,right;
    }

}