Sorting an Array Using Combsort
 
Published: 02 Nov 2003
Unedited - Community Contributed
Abstract
Using Combsort in VBScript to sort an array, with performance analysis.
by Niels Martin Hansen
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Article Contents:

Introduction

The other day I had to sort a rather large array. I could have used the wellknown quicksort-method, but then I remembered the combsort-method. (Unfortunately I can not remember, who has made this exellent sorting algorithm). Combsorting is very simple to implement and it is comparable in speed to quicksort, but is is not known by very many programmers.

Below is a VBscript-program where you can compare combsort to bobblesort. On my Thinkpad 570 I got the folowing results:

Number of elements to sort: Combsort Bubblesort
1000 0.25 sec 5.6 sec
1500 0.4 sec 12.0 sec
10000 3.4 sec n/a
20000 7 sec n/a
40000 17 sec n/a
60000 26 sec n/a

It is only the procedure CombSort, which is interesting. The rest is just to make it possible to measure the performance.

Code

Option Explicit
Dim M, t1, t2 
Dim A()
Dim B()

Sub initB()
  Dim i
  Randomize
  for i=0 to M
    B(i)= Rnd
  next
End Sub

Sub A_equal_B()
  Dim i
  for i=0 to M
    A(i) = B(i)
  next  
End Sub

Sub CombSort()
'This procedure will sort the array A
'using the CombSort-methode
  Dim i,j,gap,x,OK
  gap = M
  OK = True
  While OK
    'You can try other values, but 1.33 seems to be the best
    gap= Int(gap/1.33)
    If gap < 1 Then gap = 1
    OK = (gap <> 1)
    For i = 0 To M - gap
      j = i + gap
      If A(i) > A(j) Then
        x = A(i)
        A(i) = A(j)
        A(j) = x
        OK = True
      End If
    Next
  Wend
End Sub

Sub Bobblesort()
'This procedure will sort the array A
'using the Bobblesort-methode
  Dim i,j,x
  For i = 0 To M-1
    For j = 0 To M-1 - i
      If A(j) > A(j + 1) Then
        x = A(j)
        A(j) = A(j + 1)
        A(j + 1) = x
      End If
    Next
  Next
End Sub

Private Sub showA(txt)
  Dim s
  s= txt & VBCrLf
  s= s & "Time: " & t2-t1 & VBCrLf
  'Show the sorted array for small values of M
  if M<100 then s= s & join(A," * ")
  MsgBox s
End Sub


M=Clng(InputBox("Number of elements to sort: "))
ReDim A(M)
ReDim B(M)
initB()

'Combsort: 
'M=1500: sorttime about 0.4 sec
A_equal_B()
t1=Timer
Combsort()
t2=Timer
showA("CombSort:")

'Bobblesort 
'M=1500: sorttime about 12 sec
'so be careful not to use Bobblesort for large values of M
if M<=1500 then  
  A_equal_B
  t1=Timer
  Bobblesort
  t2=Timer
  showA("BobbleSort")
end if


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