给你一个整数数组 nums ，其中元素已经按升序排列，请你将其转换为一棵 平衡二叉搜索树。

示例 1：

输入：nums = [-10,-3,0,5,9]
输出：[0,-3,9,-10,null,5]
解释：[0,-10,5,null,-3,null,9] 也将被视为正确答案

方法：中序遍历，总是选择中间位置左边的数字作为根节点

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
//自己定义的build函数要放在前面
struct TreeNode* build(int* nums,int left,int right){
    if(left>right){return NULL;}
    int mid=(left+right)/2;
//创建新节点
    struct TreeNode* root =(struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->val=nums[mid];
    root->left=build(nums,left,mid-1);
    root->right=build(nums,mid+1,right);
    return root;
}


struct TreeNode* sortedArrayToBST(int* nums, int numsSize) {
    return build(nums,0,numsSize-1);
}