Java算法系列11 — 回顾将数组转为二叉树+从二叉树顶点逐层打印所有结点数据

1、将有序数组转为二叉树

 public static BITNode arrayToTree(int[] arr,int start,int end){
        BITNode root = null;
        if(end >= start){
            root = new BITNode();
            int mid = (start + end + 1)/2;
            //二叉树根节点为数组中间的元素
            root.data = arr[mid];
            //递归方法用左半部分数组构造root的左子树
            root.lchild = arrayToTree(arr,start,mid-1);
            //递归方法用右半部分数组构造root的右子树
            root.rchild = arrayToTree(arr,mid+1,end);
        }else{
            root = null;
        }
        return root;
    }

2、从二叉树顶点逐层打印所有结点数据

public static void printTreeLayer(BITNode root){
        if(root == null){
            return;
        }
        BITNode p;
        LinkedList<BITNode> queue = new LinkedList<>();
        //根节点入队列
        queue.offer(root);
        while(queue.size() > 0) {
            //根节点出队列，它的子节点不为空则进入队列
            p = queue.poll();
            System.out.print(p.data+" ");
            if(p.lchild != null)
            queue.offer(p.lchild);
            if(p.rchild != null)
            queue.offer(p.rchild);
        }
    }

3、测试

public static void main(String[] args) {
        int[] arr = {1,2,3,4,5,6,7,8,9,10};
        System.out.print("数组： ");
        for(int i:arr){
            System.out.print(i+" ");
        }
        System.out.println();
        BITNode root = arrayToTree(arr,0,arr.length-1);
        System.out.println();
        System.out.println("逐层打印：");
        printTreeLayer(root);
    }