leetcode------Convert Sorted Array to Binary Search Tree

标题：	Convert Sorted Array to Binary Search Tree
通过率：	33.8%
难度：	中等

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

给定的数组是递增的，那么平衡的二叉树一定是从中间开始，左树递归，右树右递归。看代码

 1 /**

 2  * Definition for binary tree

 3  * public class TreeNode {

 4  *     int val;

 5  *     TreeNode left;

 6  *     TreeNode right;

 7  *     TreeNode(int x) { val = x; }

 8  * }

 9  */

10 public class Solution {

11     public TreeNode sortedArrayToBST(int[] num) {

12         return buildTree(num,0,num.length-1);

13     }

14     public TreeNode buildTree(int[] num,int left,int right){

15         if(left>right)return null;

16         int mid=(left+right)/2;

17         TreeNode root=new TreeNode(num[mid]);

18         root.left=buildTree(num,left,mid-1);

19         root.right=buildTree(num,mid+1,right);

20         return root;

21     }

22 }