timsort (original) (raw)

Joshua Bloch jjb at google.com
Tue Jul 7 19:02:52 UTC 2009

Chris,

1) Should we update the Arrays class description and appropriate sort methods to now refer to timsort instead of saying: "The sorting algorithm is a modified mergesort...". I know this is not strictly necessary, but you must have considered it already, right? No. I totally missed it. Good catch!

I propose this prose:

 * Implementation note: This implementation is a stable, adaptive,

iterative * mergesort that requires far fewer than n lg(n) comparisons when the input * array is partially sorted, while offering the performance of a traditional * mergesort when the input array is randomly ordered. If the input array is * nearly sorted, the implementation requires approximately n comparisons. * Temporary storage requirements vary from a small constant for nearly sorted * input arrays to n/2 object references for randomly ordered input arrays. * *

The implementation takes equal advantage of ascending and descending order * in its input array, and can take advantage of ascending and descending order * in different parts of the the same input array. It is well-suited to * merging two or more sorted arrays: simply concatenate the arrays and sort * the resulting array. * *

The implementation was adapted from Tim Peters's list sort for Python * ( * TimSort). It uses techiques from Peter McIlroy's "Optimistic Sorting * and Information Theoretic Complexity",in Proceedings of the Fourth Annual * ACM-SIAM Symposium on Discrete Algorithms, pp 467-474, January 1993.

There are six methods that could use this prose, four in java.uti.Arrays, and two in java.util.Collections. Alternatively, the prose could be included in one place, and linked to repeatedly.

        Josh

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