TreeNode* sortedArrayToBST(vector<int>& nums) {
return reBuild(nums, 0, nums.size()-1);
TreeNode* reBuild(vector<int>& nums, int left, int right)
int mid = (left+right)/2;
TreeNode * root = new TreeNode(nums[mid]);
root->left = reBuild(nums, left, mid-1);
root->right = reBuild(nums, mid+1, right);