void delete(HashTable ht, Key k)
{
   int N = ht->nslots;
   Item *a = ht->items;
   int i, j, h = hash(k,N);
   for (j = 0; j < N; j++) {
      i = (h+j)%N;
      if (a[i] == NoItem) return; // k not in table
      if (eq(k,key(a[i]))) break;
   }
   a[i] = NoItem;
   ht->nitems--;
   // clean up probe path
   j = i+1;
   while (a[j] != NoItem) {
      Item it = a[j];
      a[j] = NoItem;
      ht->nitems--;
      insert(ht, it);
      j = (j+1)%N;
   }
}