JAva-Google面接問題-ソート配列を指定し、ツリーを構築する方法

import java.util.LinkedList;

public class CreateBSTfromSortedArray {

	/**
	 *  : ， 
	 *  
	 */

	public static void main(String[] args) {
		int[] data = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
		CreateBSTfromSortedArray bst = new CreateBSTfromSortedArray();
		Node root = bst.createBST(data);
		bst.inOrder(root);
		System.out.println();
		bst.levelOrder(root);
	}

	public Node createBST(int[] data) {
		if (data == null || data.length == 0) {
			return null;
		}
		Node[] nodes = createNode(data);
		return createBSTHelp(nodes, 0, data.length - 1);
	}

	//Recursion.Node[start...end],find its root.Then find left child and right child for the root.
	public Node createBSTHelp(Node[] nodes, int start, int end) {
		if (start > end) {
			return null;
		}
		int mid = start + (end - start) / 2;
		if (start == end) {
			return nodes[mid];
		}
		Node root = nodes[mid];
		root.left = createBSTHelp(nodes, start, mid - 1);
		root.right = createBSTHelp(nodes, mid + 1, end);
		return root;

	}

	public Node[] createNode(int[] data) {
		int len = data.length;
		Node[] nodes = new Node[len];
		for (int i = 0; i < len; i++) {
			nodes[i] = new Node(data[i]);
		}
		return nodes;
	}

	private static class Node {
		int data;
		Node left;
		Node right;

		Node(int data) {
			this.data = data;
		}
	}

	public void levelOrder(Node node) {
		if (node == null)
			return;
		LinkedList<Node> queue = new LinkedList<Node>();
		queue.addLast(node);
		while (!queue.isEmpty()) {
			Node curNode = queue.removeFirst();
			System.out.print(curNode.data + " ");
			if (curNode.left != null) {
				queue.addLast(curNode.left);
			}
			if (curNode.right != null) {
				queue.addLast(curNode.right);
			}
		}
	}

	public void inOrder(Node node) {
		if (node == null) {
			return;
		}
		inOrder(node.left);
		System.out.print(node.data + " ");
		inOrder(node.right);
	}

}