Ceil_From_BST.cpp

int findCeil(BinaryTreeNode<int> *root, int X)
{
    // inorder traversal
    // Iterative Approach
    int ans = -1;
    bool flag = true;
    BinaryTreeNode<int> *curr = root;
    while (curr != NULL)
    {
        if (curr->left == NULL)
        {
            if ((curr->data >= X) && flag)
            {
                ans = curr->data;
                flag = false;
            }
            curr = curr->right;
        }
        else
        {
            BinaryTreeNode<int> *pred = curr->left;
            while (pred->right != NULL && pred->right != curr)
            {
                pred = pred->right;
            }
            if (pred->right == NULL)
            {
                pred->right = curr;
                curr = curr->left;
            }
            else
            {
                if ((curr->data >= X) && flag)
                {
                    ans = curr->data;
                    flag = false;
                }
                pred->right = NULL;
                curr = curr->right;
            }
        }
    }
    return ans;
}