/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* sortedArrayToBST(vector<int>& nums) {
        if(nums.size() == 0)//有可能直接输入空数组
            return NULL;
        if(nums.size() == 1)//边界条件
            return new TreeNode(nums[0]);
        int inter = nums.size()/2;
        TreeNode* node = new TreeNode(nums[inter]);//使用new语句返回该节点的地址，而不是直接创建
        vector<int> left_array(nums.begin(), nums.begin()+inter);//创建子数组
        vector<int> right_array(nums.begin()+inter+1, nums.end());
        node->left = sortedArrayToBST(left_array);//node是指针而不是节点本身，所以要用->
        node->right = sortedArrayToBST(right_array);
        return node;
    }
};