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#ifndef INDICES_AFTER_REMOVING_H
#define INDICES_AFTER_REMOVING_H
#include <boost/config.hpp> // STATIC_CONSTANT
#include <algorithm> //swap
#include <iterator>
// iterator wrapper. inverts boolean value.
template <class AB>
struct keep_not_marked
{
typedef keep_not_marked<AB> self_type;
AB i;
bool operator *() const
{
return !*i;
}
void operator++()
{
++i;
}
bool operator ==(self_type const& o)
{
return i==o.i;
}
};
// outputs sequence to out iterator, of new indices for each element i, corresponding to deleting element i from an array when remove[i] is true (-1 if it was deleted, new index otherwise), returning one-past-end of out (the return value = # of elements left after deletion)
template <class KEEP,class KEEPe,class O>
unsigned new_indices_keep(KEEP i, KEEPe end,O out) {
unsigned f=0;
while (i!=end)
*out++ = *i++ ? f++ : (unsigned)-1;
return f;
};
template <class It,class KeepIf,class O>
unsigned new_indices_keep_if_n(unsigned n,It i,KeepIf const& r,O out)
{
unsigned f=0;
while(n--)
*out++ = r(*i++) ? f++ : (unsigned)-1;
return f;
}
template <class KEEP,class O>
unsigned new_indices(KEEP keep,O out) {
return new_indices(keep.begin(),keep.end(),out);
}
// given a vector and a parallel sequence of bools where true means keep, keep only the marked elements while maintaining order.
// this is done with a parallel sequence to the input, marked with positions the kept items would map into in a destination array, with removed items marked with the index -1. the reverse would be more compact (parallel to destination array, index of input item that goes into it) but would require the input sequence be random access.
struct indices_after
{
BOOST_STATIC_CONSTANT(unsigned,REMOVED=(unsigned)-1);
unsigned *map; // map[i] == REMOVED if i is deleted
unsigned n_kept;
unsigned n_mapped;
template <class AB,class ABe>
indices_after(AB i, ABe end) {
init(i,end);
}
template <class Vec,class R>
void init_keep_if(Vec v,R const& r)
{
n_mapped=v.size();
if ( !n_mapped ) return;
map=(unsigned *)::operator new(sizeof(unsigned)*n_mapped);
n_kept=new_indices_keep_if_n(n_mapped,r,map);
}
template <class AB,class ABe>
void init(AB i, ABe end) {
n_mapped=end-i;
if (n_mapped>0) {
map=(unsigned *)::operator new(sizeof(unsigned)*n_mapped);
n_kept=new_indices_keep(i,end,map);
} else
map=NULL;
}
template <class A>
void init(A const& a)
{
init(a.begin(),a.end());
}
template <class A>
indices_after(A const& a)
{
init(a.begin(),a.end());
}
indices_after() : n_mapped(0) {}
~indices_after()
{
if (n_mapped)
::operator delete((void*)map);
}
bool removing(unsigned i) const
{
return map[i] == REMOVED;
}
bool keeping(unsigned i) const
{
return map[i] != REMOVED;
}
unsigned operator[](unsigned i) const
{
return map[i];
}
template <class Vec>
void do_moves(Vec &v) const
{
assert(v.size()==n_mapped);
unsigned i=0;
for (;i<n_mapped&&keeping(i);++i) ;
for(;i<n_mapped;++i)
if (keeping(i))
v[map[i]]=v[i];
v.resize(n_kept);
}
template <class Vec>
void do_moves_swap(Vec &v) const
{
using std::swap;
assert(v.size()==n_mapped);
unsigned r=n_mapped;
unsigned i=0;
for (;i<n_mapped&&keeping(i);++i) ;
for(;i<n_mapped;++i)
if (keeping(i))
std::swap(v[map[i]],v[i]);
v.resize(n_kept);
}
template <class Vecto,class Vecfrom>
void copy_to(Vecto &to,Vecfrom const& v) const {
to.resize(n_kept);
for (unsigned i=0;i<n_mapped;++i)
if (keeping(i))
to[map[i]]=v[i];
}
//transform collection of indices into what we're remapping. (input/output iterators)
template <class IndexI,class IndexO>
void reindex(IndexI i,IndexI const end,IndexO o) const {
for(;i<end;++i) {
unsigned m=map[*i];
if (m!=REMOVED)
*o++=m;
}
}
template <class VecI,class VecO>
void reindex_push_back(VecI const& i,VecO &o) const {
reindex(i.begin(),i.end(),std::back_inserter(o));
}
private:
indices_after(indices_after const&)
{
map=NULL;
}
};
#endif
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