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How to do a reverse sort (descending) of filenames using Quicksort function
Posted on 2006-10-26
I'm having a problem trying to do a reverse sort (descending order; Z to A; n to 0).
The Quicksort function (mentioned below) does a sort in ascending order (A to Z; 0 to n) and is an excerpt from a C++ book called "Data Abstractions & Structures using C++". I've used the following code to do a sort of filenames/folders in a customized Enhanced Browser Page for IIS 5.0 and WORKS!!! I've tried to manipulate variables within the function to do a reverse sort however I've had no luck....
My question: How/What do I change the Quicksort function (execerpt below) to sort in descending order (Z to A; n to 0)?
'___________________________________________________________________
Sub QuickSort(vec,loBound,hiBound,SortField)
'==--------------------------------------------------------==
'== Sort a 2 dimensional array on SortField ==
'== ==
'== This procedure is adapted from the algorithm given in: ==
'== ~ Data Abstractions & Structures using C++ by ~ ==
'== ~ Mark Headington and David Riley, pg. 586 ~ ==
'== Quicksort is the fastest array sorting routine For ==
'== unordered arrays. Its big O is n log n ==
'== ==
'== Parameters: ==
'== vec - array to be sorted ==
'== SortField - The field to sort on (2nd dimension value) ==
'== loBound and hiBound are simply the upper and lower ==
'== bounds of the array's 1st dimension. It's probably ==
'== easiest to use the LBound and UBound functions to ==
'== Set these. ==
'==--------------------------------------------------------==
Dim pivot(),loSwap,hiSwap,temp,counter
Redim pivot (Ubound(vec,2))
'== Two items to sort
if hiBound - loBound = 1 then
if vec(loBound,SortField) > vec(hiBound,SortField) then
Call SwapRows(vec,hiBound,loBound)
End If
End If
'== Three or more items to sort
For counter = 0 to Ubound(vec,2)
pivot(counter) = vec(int((loBound + hiBound) / 2),counter)
vec(int((loBound + hiBound) / 2),counter) = vec(loBound,counter)
vec(loBound,counter) = pivot(counter)
Next
'loSwap = loBound + 1
'hiSwap = hiBound
loSwap = loBound + 1
hiSwap = hiBound
Do
'== Find the right loSwap
while loSwap < hiSwap and vec(loSwap,SortField) <= pivot(SortField)
loSwap = loSwap + 1
wend
'== Find the right hiSwap
while vec(hiSwap,SortField) > pivot(SortField)
hiSwap = hiSwap - 1
wend
'== Swap values if loSwap is less then hiSwap
if loSwap < hiSwap then Call SwapRows(vec,loSwap,hiSwap)
Loop While loSwap < hiSwap
For counter = 0 to Ubound(vec,2)
vec(loBound,counter) = vec(hiSwap,counter)
vec(hiSwap,counter) = pivot(counter)
Next
'== Recursively call function .. the beauty of Quicksort
'== 2 or more items in first section
if loBound < (hiSwap - 1) then Call QuickSort(vec,loBound,hiSwap-1,SortField)
'== 2 or more items in second section
if hiSwap + 1 < hibound then Call QuickSort(vec,hiSwap+1,hiBound,SortField)
End Sub 'QuickSort