If two items have the same primary key, the tie is broken using the secondary key, so no two items are ever considered equal. Finished in postorder. For example, if you want to find the item less than or equal to 5 that's closest to 5.
Hash tables can only do exact matches.
Hence, there's no way to readjust the pointers so they still point to the right chunks. Using an in-place insertion sort implementation that searches from the end of the sorted array, the remaining keys will never get past the zero. You'll wind up with two consecutive sorted portions. Radix sort uses no comparisons at all, so the zapped item doesn't affect how the others are ordered. If there's fewer than two elements, do nothing.