To find largest element smaller than K in a BST

Question

Given a binary search tree and an integer K, i would like to find the largest element less than K.

In the below tree,

for K = 13, result = 12
for K =         


        

Answer 1

I think the idea here is to record the last node after which you move to the right subtree. Therefore, the code will be (has been updated)

int findNum (Node *node, int K)
{
    Node* last_right_move = NULL;

    while (node)
    {
        if (K<=node->data)
            node = node->left;
        else
        {
            last_right_move = node;
            node = node->right;
        }
    }

    if (last_right_move)
        return last_right_move->data;
    else
        return NOT_FOUND;  // defined previously. (-1 may conflict with negative number)
}