In the extreme case, this variant works similar to merge sort.

In the bottom up merge sort, the starting point assumes each run is one item long.

Merge sort is guaranteed to arrive at any one of the possible valid results.

If I remember right, Java has always used merge sort for pretty much everything, so should be fine.

Note that for merge sort, the worst case space complexity is usually .

It can sort using just three sequential files rather than the four required by merge sort.

An iteration (or pass) in ordinary merge sort involves reading and writing the entire file.

External sorting explains how merge sort is implemented with disk drives.

Merge sort parallelizes well due to use of the divide-and-conquer method.

Heapsort also competes with merge sort, which has the same time bounds.

On the other hand, merge sort has several advantages over heapsort:

Merge sort can be adapted to operate on linked lists with O(1) extra space.

Like merge sort, quicksort can also be parallelized due to its divide-and-conquer nature.

Merge sort is used in external sorting; heapsort is not.

If the four files were on four separate tape drives, watching an ordinary merge sort would show some interesting details.

For comparison, the ordinary merge sort will combine 16 runs in 4 passes using 4 files.

In the typical case, the natural merge sort may not need as many passes because there are fewer runs to merge.

One algorithm to do this (called merge sort):

Merge algorithms, computing the merge step of a merge sort.

Merge sort also has some demerits.

However, iterative, non-recursive, implementations of merge sort, avoiding method call overhead, are not difficult to code.

Some algorithms are either recursive or non-recursive, while others may be both (e.g., merge sort).

It is much less efficient on large lists than more advanced algorithms such as quicksort, heapsort, or merge sort.

Heapsort is not a stable sort; merge sort is stable.

Like merge sort, external distribution sort also has a main-memory sibling; see bucket sort.