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implementation of stabilized quicksort

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Jiri Pittner
2023-07-30 11:00:41 +02:00
parent ec42999812
commit a439e0be94
4 changed files with 92 additions and 10 deletions
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60
qsort.h
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@@ -104,6 +104,66 @@ return parity;
}
//stabilized version of quicksort employing auxiliary key of the original position
template<int type, typename SORTABLE, typename INDEX, typename PERMINDEX>
int memqsortaux(SORTABLE &object, PERMINDEX *perm, INDEX l, INDEX r, INDEX *aux)
{
INDEX i,j,piv;
int parity=0;
if(r<=l) return parity; //1 element
if(LA_sort_traits<SORTABLE,INDEX,type>::comparestable(object,l,r,aux)) {parity^=1; object.swap(l,r); {INDEX tmp=aux[l]; aux[l]=aux[r]; aux[r]=tmp;} if(perm) {PERMINDEX tmp=perm[l]; perm[l]=perm[r]; perm[r]=tmp;}}
if(r-l==1) return parity; //2 elements and preparation for median
piv= l+(r-l)/2; //pivoting by median of 3 - safer
if(LA_sort_traits<SORTABLE,INDEX,type>::comparestable(object,l,piv,aux)) {parity^=1; object.swap(l,piv); {INDEX tmp=aux[l]; aux[l]=aux[piv]; aux[piv]=tmp;} if(perm) {PERMINDEX tmp=perm[l]; perm[l]=perm[piv]; perm[piv]=tmp;}} //and change the pivot element implicitly
if(LA_sort_traits<SORTABLE,INDEX,type>::comparestable(object,piv,r,aux)) {parity^=1; object.swap(r,piv); {INDEX tmp=aux[r]; aux[r]=aux[piv]; aux[piv]=tmp;} if(perm) {PERMINDEX tmp=perm[r]; perm[r]=perm[piv]; perm[piv]=tmp;}} //and change the pivot element implicitly
if(r-l==2) return parity; //in the case of 3 elements we are finished too
//general case , l-th r-th already processed
i=l+1; j=r-1;
do{
//important sharp inequality - stops at sentinel element for efficiency
// this is inefficient if all keys are equal - unnecessary n log n swaps are done, but we assume that it is atypical input
while(LA_sort_traits<SORTABLE,INDEX,type>::comparestable(object,piv,i++,aux));
i--;
while(LA_sort_traits<SORTABLE,INDEX,type>::comparestable(object,j--,piv,aux));
j++;
if(i<j)
{
// swap and keep track of position of pivoting element
parity^=1;
object.swap(i,j);
{INDEX tmp =aux[i]; aux[i]=aux[j]; aux[j]=tmp;}
if(perm) {PERMINDEX tmp=perm[i]; perm[i]=perm[j]; perm[j]=tmp;}
if(i==piv) piv=j; else if(j==piv) piv=i;
}
if(i<=j) {i++; j--;}
}while(i<=j);
if(j-l < r-i) //because of the stack in bad case process first the shorter subarray
{if(l<j) parity ^=memqsortaux<type,SORTABLE,INDEX,PERMINDEX>(object,perm,l,j,aux); if(i<r) parity ^=memqsortaux<type,SORTABLE,INDEX,PERMINDEX>(object,perm,i,r,aux);}
else
{if(i<r) parity ^=memqsortaux<type,SORTABLE,INDEX,PERMINDEX>(object,perm,i,r,aux); if(l<j) parity ^=memqsortaux<type,SORTABLE,INDEX,PERMINDEX>(object,perm,l,j,aux);}
return parity;
}
template<int type, typename SORTABLE, typename INDEX, typename PERMINDEX>
int memqsortstable(SORTABLE &object, PERMINDEX *perm, INDEX l, INDEX r)
{
if(r<=l) return 0; //1 element
INDEX *aux= new INDEX[r-l+1];
if(aux==NULL) laerror("allocation failed in memqsortstable");
INDEX *auxshifted = aux-l;
for(INDEX i=l; i<=r; ++i) auxshifted[i]=i;
int parity=memqsortaux<type,SORTABLE,INDEX,PERMINDEX>(object,perm,l,r,auxshifted);
delete[] aux;
return parity;
}
template<typename S, typename PERMINDEX>
int ptrqsortup(S *l, S *r, PERMINDEX *perm=NULL)
{