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/*=========================================================================
*
* Copyright NumFOCUS
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0.txt
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*=========================================================================*/
#ifndef itkEquivalencyTable_h
#define itkEquivalencyTable_h
#include "itkProcessObject.h"
#include <unordered_map>
namespace itk
{
/** \class EquivalencyTable
* \brief Hash table to manage integral label equivalencies
*
* EquivalencyTable is a hash table for recording equivalencies among
* unsigned long integer values. EquivalencyTable can store recursive
* relationships (8=7, 7=6, 6=5, ...) or be "flattened" to eliminate
* recursion. The table uses an efficient algorithm for eliminating
* redundancy and preventing circular dependencies.
*
* \par
* In the context of the watershed segmentation algorithm
* (itk::WatershedImageFilter), this table is used to store connections
* identified among image segments and as the input to
* itk::watershed::Relabeler.
* \ingroup WatershedSegmentation
* \ingroup ITKCommon
*/
class ITKCommon_EXPORT EquivalencyTable : public DataObject
{
public:
ITK_DISALLOW_COPY_AND_MOVE(EquivalencyTable);
/** Standard smart pointer declarations */
using Self = EquivalencyTable;
using Superclass = DataObject;
using Pointer = SmartPointer<Self>;
using ConstPointer = SmartPointer<const Self>;
itkNewMacro(Self);
itkOverrideGetNameOfClassMacro(EquivalencyTable);
/** Define the container type for the table. */
using HashTableType = std::unordered_map<unsigned long, unsigned long, std::hash<unsigned long>>;
using Iterator = HashTableType::iterator;
using ConstIterator = HashTableType::const_iterator;
using ValueType = HashTableType::value_type;
/** "Flattens" the equivalency table by eliminating all redundant
* and recursive equivalencies. I.e. the set { 2=1; 3=2; 4=3 } is
* converted to {4=1; 3=1; 2=1}. */
void
Flatten();
/** Insert an equivalency into the table. A return value of TRUE
* indicates that the equivalency did not previously exist in the
* table and was successfully added. A FALSE return value indicates
* that the equivalency was not added to the table because a
* conflict with an existing entry occurred (most likely, the
* equivalency was already recorded directly or indirectly). */
bool
Add(unsigned long a, unsigned long b);
/** Insert an equivalency into the table and flatten that
* equivalency. A return value of TRUE indicates that the
* equivalency did not previously exist in the table and was
* successfully added. A FALSE return value indicates that the
* equivalency was not added to the table because a conflict with an
* existing entry occurred (most likely, the equivalency was already
* recorded directly or indirectly). */
bool
AddAndFlatten(unsigned long a, unsigned long b);
/** Lookup an equivalency in the table. If no entry is found in the
* table, the method returns its the value of the argument. Does
* not recursively descent through equivalencies. */
unsigned long
Lookup(const unsigned long a) const
{
auto result = m_HashMap.find(a);
if (result == m_HashMap.end())
{
return a;
}
else
{
return result->second;
}
}
/** Lookup an equivalency in the table by recursing through all
* successive equivalencies. For example, if the follow entries
* exist in the table {8=7, 7=6, 6=5}, then RecursiveLookup(8)
* returns 5. */
unsigned long
RecursiveLookup(const unsigned long a) const;
/** Returns TRUE if the label is found in the table and FALSE is the label is
* not found in the table. */
bool
IsEntry(const unsigned long a) const
{
if (m_HashMap.find(a) == m_HashMap.end())
{
return false;
}
else
{
return true;
}
}
/** Erases the entry with key a. */
void
Erase(const unsigned long a)
{
m_HashMap.erase(a);
}
/** Erases all the entries in the table. */
void
Clear()
{
m_HashMap.clear();
}
/** Returns TRUE if the table is empty, FALSE if it is not empty. */
bool
Empty() const
{
return m_HashMap.empty();
}
/** Returns the number of entries in the table. */
HashTableType::size_type
Size() const
{
return m_HashMap.size();
}
/** Returns an iterator pointing to the first element of the (unordered)
* table. */
Iterator
Begin()
{
return m_HashMap.begin();
}
/** Returns and iterator pointing to one position past the last
* element of the (unordered) table. */
Iterator
End()
{
return m_HashMap.end();
}
/** Convenience method for debugging. */
// void PrintHashTable();
protected:
EquivalencyTable() = default;
~EquivalencyTable() override = default;
void
PrintSelf(std::ostream & os, Indent indent) const override;
HashTableType m_HashMap{};
};
} // end namespace itk
#endif
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