operations_research::SparsePermutation Class Reference

A compact representation for permutations of {0..N-1} that displaces few elements: it needs only O(K) memory for a permutation that displaces K elements. More...

#include <sparse_permutation.h>

Classes
struct	Iterator

Public Member Functions
	SparsePermutation (int size)
int	Size () const
int	NumCycles () const
const std::vector< int > &	Support () const
	Returns the "support" of this permutation; that is, the set of elements displaced by it. More...
Iterator	Cycle (int i) const
int	LastElementInCycle (int i) const
	This is useful for iterating over the pair {element, image} of a permutation: More...
void	AddToCurrentCycle (int x)
	To add a cycle to the permutation, repeatedly call AddToCurrentCycle() with the cycle's orbit, then call CloseCurrentCycle(); This shouldn't be called on trivial cycles (of length 1). More...
void	CloseCurrentCycle ()
void	RemoveCycles (const std::vector< int > &cycle_indices)
	Removes the cycles with given indices from the permutation. More...
std::string	DebugString () const
	Output all non-identity cycles of the permutation, sorted lexicographically (each cycle is described starting by its smallest element; and all cycles are sorted lexicographically against each other). More...

Detailed Description

A compact representation for permutations of {0..N-1} that displaces few elements: it needs only O(K) memory for a permutation that displaces K elements.

Definition at line 27 of file sparse_permutation.h.

Constructor & Destructor Documentation

SparsePermutation()

operations_research::SparsePermutation::SparsePermutation ( int  size )

inlineexplicit

Definition at line 29 of file sparse_permutation.h.

Member Function Documentation

AddToCurrentCycle()

void operations_research::SparsePermutation::AddToCurrentCycle ( int  x )

inline

To add a cycle to the permutation, repeatedly call AddToCurrentCycle() with the cycle's orbit, then call CloseCurrentCycle(); This shouldn't be called on trivial cycles (of length 1).

Definition at line 84 of file sparse_permutation.h.

CloseCurrentCycle()

void operations_research::SparsePermutation::CloseCurrentCycle ( )

inline

Definition at line 90 of file sparse_permutation.h.

Cycle()

SparsePermutation::Iterator operations_research::SparsePermutation::Cycle ( int  i ) const

inline

Definition at line 117 of file sparse_permutation.h.

DebugString()

std::string operations_research::SparsePermutation::DebugString

(

)

const

Output all non-identity cycles of the permutation, sorted lexicographically (each cycle is described starting by its smallest element; and all cycles are sorted lexicographically against each other).

This isn't efficient; use for debugging only. Example: "(1 4 3) (5 9) (6 8 7)".

LastElementInCycle()

int operations_research::SparsePermutation::LastElementInCycle ( int  i ) const

inline

This is useful for iterating over the pair {element, image} of a permutation:

for (int c = 0; c < perm.NumCycles(); ++c) { int element = LastElementInCycle(c); for (int image : perm.Cycle(c)) { ///< The pair is (element, image). ... element = image; } }

Todo:

(user): Provide a full iterator for this? Note that we have more information with the loop above. Not sure it is needed though.

Definition at line 124 of file sparse_permutation.h.

NumCycles()

int operations_research::SparsePermutation::NumCycles ( ) const

inline

Definition at line 33 of file sparse_permutation.h.

RemoveCycles()

void operations_research::SparsePermutation::RemoveCycles

(

const std::vector< int > &

cycle_indices

)

Removes the cycles with given indices from the permutation.

This works in O(K) for a permutation displacing K elements.

Size()

int operations_research::SparsePermutation::Size ( ) const

inline

Todo:

(user,user): complete the reader API.

Definition at line 32 of file sparse_permutation.h.

Support()

const std::vector<int>& operations_research::SparsePermutation::Support ( ) const

inline

Returns the "support" of this permutation; that is, the set of elements displaced by it.

Definition at line 37 of file sparse_permutation.h.

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

• sparse_permutation.h