common_ancestor.c

struct node
{
    int info;
    struct node *left;
    struct node *right;
};

struct node *common_ancestor(struct node *head, struct node* n1,
                             struct node *n2)
{
    return common_helper(head, n1, n2, NULL);
}
                             
struct node *common_helper(struct node *head, struct node *n1, 
                           struct node *n2, struct node *parent)
{
    

    if (head == NULL)
        return NULL;
    else if ((n1->info > head->info && n2->info < head->info) ||
        (n1->info < head->info && n2->info > head->info))
        return head;
    else if (n1->info < head->info && n2->info < head->info) {
        return common_ancestor(head->left, n1, n2, head);
    }
    else if (n1->info > head->info && n2->info > head->info) {
       return common_ancestor(head>right, n1, n2, head);
    }
    else {
        return parent;
    }
}