Question

Write a Java method to delete a record from a B-tree of order n.

Answer 1

Answer:

Deleting a record on a B-tree consists of three main events:

- Searching the node where the key to be deleted exists

- Deleting the key

- Balancing the tree if required

Explanation:

q = NULL;

   p = tree;

   while (p) {

       i = nodesearch(p, key);

       q = p;

       if (i < used(p) -1 && key == k(p,i)) {

           found = TRUE;

           position = i;

           break;

       }

       p = son(p,i);

   }

   if (!found)

   else if (subtree(p)) {

         if (used(p) > ((n-1)/2)+1)

         delkey (p, position, key);

       else {

           replace (p, position, fsucc(p));

           p0 r1 p1 r2 p2 r3 ……. pn-1 rn-1 pn

           q = &fsucc(p);

           qpos = index of fsucc;

           if (used(rbrother(p)) > ((n-1)/2)+1)

               replace (q, qpos, sonsucc(q));

           else

               while (q && used(q) < (n-1)/2) {

                   concatenate(q, brother(q));

                   q = father(q);

               }

       }

   }

   else

   delkey(p, position, key);

}