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

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode sortedArrayToBST(int[] num) {
        return buildTree(num,0,num.length-1);
    }
    public TreeNode buildTree(int[] num,int left,int right){
        if(left>right)return null;
        int mid=(left+right)/2;
        TreeNode root=new TreeNode(num[mid]);
        root.left=buildTree(num,left,mid-1);
        root.right=buildTree(num,mid+1,right);
        return root;
    }
}