// Copyright (C) 2021 Jakub Melka
//
// This file is part of PDF4QT.
//
// PDF4QT is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// with the written consent of the copyright owner, any later version.
//
// PDF4QT is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with PDF4QT. If not, see <https://www.gnu.org/licenses/>.
#ifndef PDFALGORITHMLCS_H
#define PDFALGORITHMLCS_H
#include "pdfglobal.h"
namespace pdf
{
class PDFAlgorithmLongestCommonSubsequenceBase
{
public:
enum SequenceItemFlag
{
None = 0x0000,
MovedLeft = 0x0001, ///< Item has been moved from this position (is present in a sequence no. 1)
MovedRight = 0x0002, ///< Item has been moved to this position (is present in a sequence no. 2)
Moved = 0x0004, ///< Index of item has been changed
Added = 0x0008, ///< Item has been added to a sequence no. 2
Removed = 0x0010, ///< Item has been removed from a sequence no. 1
Replaced = 0x0020, ///< Item has been replaced (or sequence of items has been replaced)
};
Q_DECLARE_FLAGS(SequenceItemFlags, SequenceItemFlag)
struct SequenceItem
{
size_t index1 = std::numeric_limits<size_t>::max();
size_t index2 = std::numeric_limits<size_t>::max();
SequenceItemFlags flags = None;
bool isLeftValid() const { return index1 != std::numeric_limits<size_t>::max(); }
bool isRightValid() const { return index2 != std::numeric_limits<size_t>::max(); }
bool isLeft() const { return isLeftValid() && !isRightValid(); }
bool isRight() const { return isRightValid() && !isLeftValid(); }
bool isMatch() const { return isLeftValid() && isRightValid(); }
bool isMovedLeft() const { return flags.testFlag(MovedLeft); }
bool isMovedRight() const { return flags.testFlag(MovedRight); }
bool isMoved() const { return flags.testFlag(Moved); }
bool isAdded() const { return flags.testFlag(Added); }
bool isRemoved() const { return flags.testFlag(Removed); }
bool isReplaced() const { return flags.testFlag(Replaced); }
bool isModified() const { return isAdded() || isRemoved() || isReplaced(); }
void markMovedLeft() { flags.setFlag(MovedLeft); }
void markMovedRight() { flags.setFlag(MovedRight); }
void markMoved() { flags.setFlag(Moved); }
void markAdded() { flags.setFlag(Added); }
void markRemoved() { flags.setFlag(Removed); }
void markReplaced() { flags.setFlag(Replaced); }
};
using Sequence = typename std::vector<SequenceItem>;
using SequenceIterator = typename Sequence::iterator;
using SequenceItemRange = typename std::pair<SequenceIterator, SequenceIterator>;
using SequenceItemRanges = typename std::vector<SequenceItemRange>;
/// Marks a sequence with set of flags representing added/removed/replaced/moved
/// items. Moved items sequences must be sorted.
/// \param sequence Sequence to be marked
/// \param movedItemsLeft Sorted sequence of left indices, which have been moved
/// \param movedItemsRight sorted sequence of right indices, which have been moved
static void markSequence(Sequence& sequence,
const std::vector<size_t>& movedItemsLeft,
const std::vector<size_t>& movedItemsRight);
/// Returns item ranges, which should be checked - for example,
/// for text modification.
/// \param sequence Sequence
static SequenceItemRanges getModifiedRanges(Sequence& sequence);
/// Collect flags from given item range
/// \param range Range
static SequenceItemFlags collectFlags(const SequenceItemRange& range);
};
/// Algorithm for computing longest common subsequence, on two sequences
/// of objects, which are implementing operator "==" (equal operator).
/// Constructor takes bidirectional iterators to the sequence. So, iterators
/// are requred to be bidirectional.
template<typename Iterator, typename Comparator>
class PDFAlgorithmLongestCommonSubsequence : public PDFAlgorithmLongestCommonSubsequenceBase
{
public:
PDFAlgorithmLongestCommonSubsequence(Iterator it1,
Iterator it1End,
Iterator it2,
Iterator it2End,
Comparator comparator);
void perform();
const Sequence& getSequence() const { return m_sequence; }
private:
Iterator m_it1;
Iterator m_it1End;
Iterator m_it2;
Iterator m_it2End;
size_t m_size1;
size_t m_size2;
size_t m_matrixSize;
Comparator m_comparator;
std::vector<bool> m_backtrackData;
Sequence m_sequence;
};
template<typename Iterator, typename Comparator>
PDFAlgorithmLongestCommonSubsequence<Iterator, Comparator>::PDFAlgorithmLongestCommonSubsequence(Iterator it1,
Iterator it1End,
Iterator it2,
Iterator it2End,
Comparator comparator) :
m_it1(std::move(it1)),
m_it1End(std::move(it1End)),
m_it2(std::move(it2)),
m_it2End(std::move(it2End)),
m_size1(0),
m_size2(0),
m_matrixSize(0),
m_comparator(std::move(comparator))
{
m_size1 = std::distance(m_it1, m_it1End) + 1;
m_size2 = std::distance(m_it2, m_it2End) + 1;
m_matrixSize = m_size1 * m_size2;
}
template<typename Iterator, typename Comparator>
void PDFAlgorithmLongestCommonSubsequence<Iterator, Comparator>::perform()
{
m_backtrackData.resize(m_matrixSize);
m_sequence.clear();
std::vector<size_t> rowTop(m_size1, size_t());
std::vector<size_t> rowBottom(m_size1, size_t());
// Jakub Melka: we will have columns consisting of it1...it1End
// and rows consisting of it2...it2End. We iterate trough rows,
// and for each row, we update longest common subsequence data.
auto it2 = m_it2;
for (size_t i2 = 1; i2 < m_size2; ++i2, ++it2)
{
auto it1 = m_it1;
for (size_t i1 = 1; i1 < m_size1; ++i1, ++it1)
{
if (m_comparator(*it1, *it2))
{
// We have match
rowBottom[i1] = rowTop[i1 - 1] + 1;
}
else
{
const size_t leftCellValue = rowBottom[i1 - 1];
const size_t upperCellValue = rowTop[i1];
bool isLeftBigger = leftCellValue > upperCellValue;
if (isLeftBigger)
{
rowBottom[i1] = leftCellValue;
m_backtrackData[i2 * m_size1 + i1] = true;
}
else
{
rowBottom[i1] = upperCellValue;
m_backtrackData[i2 * m_size1 + i1] = false;
}
}
}
// Bottom row will become top row
std::swap(rowTop, rowBottom);
}
size_t i1 = m_size1 - 1;
size_t i2 = m_size2 - 1;
while (i1 > 0 && i2 > 0)
{
SequenceItem item;
const size_t index1 = i1 - 1;
const size_t index2 = i2 - 1;
auto cit1 = std::next(m_it1, index1);
auto cit2 = std::next(m_it2, index2);
if (m_comparator(*cit1, *cit2))
{
item.index1 = index1;
item.index2 = index2;
--i1;
--i2;
}
else
{
if (m_backtrackData[i2 * m_size1 + i1])
{
item.index1 = index1;
--i1;
}
else
{
item.index2 = index2;
--i2;
}
}
m_sequence.push_back(item);
}
while (i1 > 0)
{
SequenceItem item;
const size_t index1 = i1 - 1;
item.index1 = index1;
--i1;
m_sequence.push_back(item);
}
while (i2 > 0)
{
SequenceItem item;
const size_t index2 = i2 - 1;
item.index2 = index2;
--i2;
m_sequence.push_back(item);
}
std::reverse(m_sequence.begin(), m_sequence.end());
}
} // namespace pdf
#endif // PDFALGORITHMLCS_H