Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.java.programmer > #10498

Re: Verifying a list is alphabetized

Show all headers | View raw

On Sat, 3 Dec 2011, Roedy Green wrote:

> On Sat, 03 Dec 2011 20:05:24 -0800, Roedy Green
> <see_website@mindprod.com.invalid> wrote, quoted or indirectly quoted
> someone who said :
>
>> It does do a check first if things are in order.
>
> No. Sun's sort does NOT check first.

Yes, it does. The scripture:

http://docs.oracle.com/javase/6/docs/api/java/util/Arrays.html#sort%28java.lang.Object[]%29

States:

  The sorting algorithm is a modified mergesort (in which the merge is
  omitted if the highest element in the low sublist is less than the lowest
  element in the high sublist).

That bit about the omission of the merge means that if the input is 
sorted, then there will be no actual attempt at sorting; the merges will 
all be skipped. That behaviour is not only the way things are, it's 
guaranteed by the docs.

If you take a look at the actual implementation, there is a method called 
mergeSort on line 1146 of Arrays.java which does the dirty work:

http://hg.openjdk.java.net/jdk6/jdk6-gate/jdk/file/tip/src/share/classes/java/util/Arrays.java

It is a classical recursive mergesort. For sublists smaller than seven 
elements, it does an insertion sort; insertion sort is itself adaptive, in 
that on a sorted input, it will make a single pass through the list, 
noticing that the elements are in order, and not moving any of them. O(n) 
with a minimal constant - or, if you like, O(7), with O(n/7) calls, which 
is O(n) over the whole list. For larger sublists, there is the 
aforementioned already-ordered check; that's O(1) per check, and there 
are, i think O(log n) checks made during the 'merge'. So, O(n) overall, 
with most of the time spent in checks in the insertion sort.

tom

-- 
So the moon is approximately 24 toasters from Scunthorpe.

Back to comp.lang.java.programmer | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Verifying a list is alphabetized laredotornado <laredotornado@zipmail.com> - 2011-11-30 07:52 -0800
  Re: Verifying a list is alphabetized Knute Johnson <nospam@knutejohnson.com> - 2011-11-30 08:05 -0800
    Re: Verifying a list is alphabetized Lew <lewbloch@gmail.com> - 2011-11-30 11:18 -0800
    Re: Verifying a list is alphabetized Arne Vajhøj <arne@vajhoej.dk> - 2011-12-02 19:54 -0500
      Re: Verifying a list is alphabetized Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-12-03 07:44 -0500
        Re: Verifying a list is alphabetized Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-12-03 09:02 -0500
        Re: Verifying a list is alphabetized Roedy Green <see_website@mindprod.com.invalid> - 2011-12-03 20:05 -0800
          Re: Verifying a list is alphabetized Roedy Green <see_website@mindprod.com.invalid> - 2011-12-03 22:13 -0800
            Re: Verifying a list is alphabetized Tom Anderson <twic@urchin.earth.li> - 2011-12-04 21:47 +0000
          Re: Verifying a list is alphabetized Martin Gregorie <martin@address-in-sig.invalid> - 2011-12-04 12:42 +0000
            Re: Verifying a list is alphabetized Patricia Shanahan <pats@acm.org> - 2011-12-04 12:18 -0800
              Re: Verifying a list is alphabetized Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-12-04 13:17 -0800
                Re: Verifying a list is alphabetized Patricia Shanahan <pats@acm.org> - 2011-12-04 15:32 -0800
                Re: Verifying a list is alphabetized markspace <-@.> - 2011-12-04 15:59 -0800
                Re: Verifying a list is alphabetized Patricia Shanahan <pats@acm.org> - 2011-12-04 16:14 -0800
                Re: Verifying a list is alphabetized markspace <-@.> - 2011-12-04 17:12 -0800
                Re: Verifying a list is alphabetized Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-12-04 21:17 -0500
            Re: Verifying a list is alphabetized Tom Anderson <twic@urchin.earth.li> - 2011-12-04 22:11 +0000
              Re: Verifying a list is alphabetized Martin Gregorie <martin@address-in-sig.invalid> - 2011-12-04 23:41 +0000
              Re: Verifying a list is alphabetized Roedy Green <see_website@mindprod.com.invalid> - 2011-12-12 01:39 -0800
          Re: Verifying a list is alphabetized Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-12-04 08:47 -0500
          Re: Verifying a list is alphabetized Gene Wirchenko <genew@ocis.net> - 2011-12-04 21:34 -0800
  Re: Verifying a list is alphabetized Patricia Shanahan <pats@acm.org> - 2011-11-30 12:52 -0800
    Re: Verifying a list is alphabetized laredotornado <laredotornado@zipmail.com> - 2011-12-01 06:43 -0800
  Re: Verifying a list is alphabetized Joshua Maurice <joshuamaurice@gmail.com> - 2011-11-30 13:16 -0800
  Re: Verifying a list is alphabetized Roedy Green <see_website@mindprod.com.invalid> - 2011-12-02 01:43 -0800
    Re: Verifying a list is alphabetized Patricia Shanahan <pats@acm.org> - 2011-12-02 05:58 -0800
      Re: Verifying a list is alphabetized Arne Vajhøj <arne@vajhoej.dk> - 2011-12-02 19:55 -0500
      Re: Verifying a list is alphabetized Roedy Green <see_website@mindprod.com.invalid> - 2011-12-03 02:54 -0800
        Re: Verifying a list is alphabetized Patricia Shanahan <pats@acm.org> - 2011-12-03 06:17 -0800
    Re: Verifying a list is alphabetized Roedy Green <see_website@mindprod.com.invalid> - 2011-12-03 03:10 -0800
  Re: Verifying a list is alphabetized Arne Vajhøj <arne@vajhoej.dk> - 2011-12-02 19:52 -0500

csiph-web