把排序数组转换为高度最小的二叉搜索树

class Solution {public:    /**     * @param A: A sorted (increasing order) array     * @return: A tree node     */     TreeNode *x;     bool xxx=1;     void look(TreeNode *&x,int minn,int maxx,vector<int> A)     {        if(minn==maxx)         return;         x=new TreeNode ;         x->val=A[(minn+maxx-1)/2];         look(x->left,minn,(minn+maxx-1)/2,A);         look(x->right,(minn+maxx-1)/2+1,maxx,A);                      }    TreeNode *sortedArrayToBST(vector<int> &A) {        int xx=A.size();        if(xx==0)        return NULL;        //x=new TreeNode;        look(x,0,xx,A);        return x;         // write your code here    }};