Molassembler  3.0.0
Molecule graph and conformer library
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Scine::Molassembler::Shapes::Partitioner Class Reference

Given S * E distinguishable objects, this class helps enumerate all partitions into S groups of size E. More...

#include <Partitioner.h>

Public Member Functions

 Partitioner (unsigned s, unsigned e)
 Constructor. More...
 
bool next_partition ()
 Advance underlying state to the next partition. More...
 
std::vector< std::vector
< unsigned > > 
partitions () const
 Generate sets of element indices within their respective partitions. More...
 
unsigned s () const
 Number of groups.
 
unsigned e () const
 Number of elements per group.
 
const std::vector< unsigned > & map () const
 Access to underlying flat map from element index to group index.
 

Static Public Member Functions

static bool isOrderedMapping (const std::vector< unsigned > &mapping)
 Check whether the sets as specified by the mapping are ordered. More...
 

Private Attributes

unsigned S
 Number of groups.
 
unsigned E
 Number of elements per group.
 
std::vector< unsigned > mapping
 Flat map from element index to group index.
 

Detailed Description

Given S * E distinguishable objects, this class helps enumerate all partitions into S groups of size E.

The challenge with writing such a class is getting complexity less than \(\Theta((S\cdot E)!)\) considering that the sets themselves are indistinguishable. For instance, for the trivial example \(S = 2, E = 2\), there are only three distinct solutions:

  • {1, 2}, {3, 4}
  • {1, 3}, {2, 4}
  • {1, 4}, {2, 3}

There are two orders at play here, the sets are lexicographically ordered and the elements within them are too.

Constructor & Destructor Documentation

Scine::Molassembler::Shapes::Partitioner::Partitioner ( unsigned  s,
unsigned  e 
)

Constructor.

Parameters
sNumber of groups
eNumber of elements per group
Precondition
s is not zero and e is not zero

Complexity \(\Theta(S\cdot E)\)

Member Function Documentation

static bool Scine::Molassembler::Shapes::Partitioner::isOrderedMapping ( const std::vector< unsigned > &  mapping)
static

Check whether the sets as specified by the mapping are ordered.

Complexity \(O(S\cdot E)\)

bool Scine::Molassembler::Shapes::Partitioner::next_partition ( )

Advance underlying state to the next partition.

Complexity \(O(S\cdot E)\)

Returns
whether the underlying state reflects a new, valid partition
std::vector< std::vector<unsigned> > Scine::Molassembler::Shapes::Partitioner::partitions ( ) const

Generate sets of element indices within their respective partitions.

Complexity \(\Theta(S\cdot E)\)


The documentation for this class was generated from the following file: