Problems with hashing:

• hash function relies on size of array (⇒ can't expand)
  • changing the size of the array changes the hash function
  • could make array larger, but would need to re-insert all Items
• items are stored in (effectively) random order
• if size(KeySpace) size(IndexSpace),  collisions inevitable
  • collision:   k != j  &&  hash(k,N) == hash(j,N)
• if nitems > nslots,  collisions inevitable