[LeetCode]Convert Sorted Array to Binary Search Tree

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

平衡二叉树：
1、若任意节点的左子树不空，则左子树上所有结点的值均小于它的根结点的值；
2、若任意节点的右子树不空，则右子树上所有结点的值均大于它的根结点的值；
3、它是一棵空树或它的左右两个子树的高度差的绝对值不超过1，并且左右两个子树都是一棵平衡二叉树

由于数组已经排序，此处我们采用二分递归法进行处理

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

        node.left=createTreeNode(nums,left,mid-1);
        node.right=createTreeNode(nums,mid+1,right);
        return node;
    }

}