Sorted Array to Balanced BST

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

TreeNode* getnode(int x)

{

    TreeNode* t = (TreeNode *)malloc(sizeof(TreeNode));

    t->val = x;

    t->left = NULL;

    t->right =NULL;

    return t;

}

TreeNode *sortedArrayToBST(vector<int> &num, int left, int right)

{

    if(left > right)

        return NULL;

    int mid = (left + right) / 2;

    TreeNode* root  = getnode(num[mid]);   

    root->left = sortedArrayToBST(num, left, mid -1);

    root->right = sortedArrayToBST(num, mid+1, right);

    return root;

}

TreeNode *sortedArrayToBST(vector<int> &num) {

        if(num.size() <= 0)

            return NULL;

    return sortedArrayToBST(num, 0, num.size() -1);

}