Quicksort Algorithm

[WildRyan]

If I understand this algorithm correctly it will sort an array (A) with p being a pointer to the first element, and r being a pointer to the last element in descending order.

1.Quicksort(A,p,r)
2. if p < r then
3. q = Partition(A,p,r)
4. Quicksort(A,p,q)
5. Quicksort(A,q+1,r)
6.Partition(A,p,r)
7.x = A[p]
8.i = p-1
9.j = r+1
10.while TRUE
11. do repeat j = j – 1
12. until A[j] >= x
13. repeat i = i + 1
14. until A <= x
15. if i < j then
16. exchange A with A[j]
17. else
18. return j


Will this work properly? I changed a generic version of quicksort by reversing the >= and the <= on lines 12,14.

 

[WildRyan]

Maybe I am in the wrong forum. I am new to tek-tips, could anyone point me in the right direction?

 

[Levis501]

Hi Ryan,
If I'm correct in assuming that you are simply trying to sort the array in reverse order, then you should be good to go with the changes you've made.
I think you've got a possible typo in lines 14 and 16. The A should be A.

As with any algorithm, I find that the best confirmation is typing up a small program to give it a whirl.

-Steve

PS: Seems like a good place to post this.

 

[benlinkknilneb]

The typo that Levis refers to is a result of TGML. In order to prevent the tags from being read, wrap any (pseudo)code in

tags. These work like HTML tags, except that they use the [] instead of <>. A more detailed description is given in the link just above &quot;Submit Post&quot; on the posting form.

Ben
A programmer was drowning. Lots of people watched but did nothing. They couldn't understand why he yelled &quot;F1!&quot;