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made worst case quicksort run nearly impossible by using a random element

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git-svn-id: http://svn.osgeo.org/qgis/trunk@279 c8812cc2-4d05-0410-92ff-de0c093fc19c
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mhugent 2003-09-16 18:21:00 +00:00
parent 78b59e91f2
commit a94e54422a
1 changed files with 4 additions and 0 deletions
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4
src/qgsattributetable.cpp
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@ -237,6 +237,10 @@ void QgsAttributeTable::qsort(int lower, int upper, int col, bool ascending, boo
QString v; QString v;
if(upper>lower) if(upper>lower)
{ {
//chose a random element (this avoids n^2 worst case)
int element=double(rand())/RAND_MAX*(upper-lower)+lower;
swapRows(element,upper);
v=text(upper,col); v=text(upper,col);
i=lower-1; i=lower-1;
j=upper; j=upper;