source: tspsg/src/tspsolver.cpp @ 9cda6e0f5d

/*
 *  TSPSG: TSP Solver and Generator
 *  Copyright (C) 2007-2010 Lёppa <contacts[at]oleksii[dot]name>
 *
 *  $Id$
 *  $URL$
 *
 *  This file is part of TSPSG.
 *
 *  TSPSG is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  TSPSG 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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with TSPSG.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "tspsolver.h"

//! \internal \brief A short for maximum double, used internally in the solution algorithm.
#define MAX_DOUBLE std::numeric_limits<double>::max()

namespace TSPSolver {

/*!
 * \brief Returns CTSPSolver's version ID.
 * \return A string: <b>\$Id$</b>.
 */
QString CTSPSolver::getVersionId()
{
        return QString("$Id$");
}

/*!
 * \brief Constructs CTSPSolver object.
 * \param parent A parent object.
 */
CTSPSolver::CTSPSolver(QObject *parent)
        : QObject(parent), nCities(0), total(0), root(NULL) {}

/*!
 * \brief Cleans up the object and frees up memory used by the solution tree.
 * \param processEvents If set to \c true then \link QCoreApplication::processEvents() QCoreApplication::processEvents(QEventLoop::ExcludeUserInputEvents)\endlink will be called from time to time while cleaning up.
 * \warning After call to this function a solution tree returned by the solve() function is no longer valid.
 * \note It is not required to call this function manually. This function is always called by solve() at the beginning of the solution process.
 *
 * \sa solve()
 */
void CTSPSolver::cleanup(bool processEvents)
{
#ifdef QAPPLICATION_H
        if (!processEvents)
                QApplication::setOverrideCursor(QCursor(Qt::WaitCursor));
#endif
        route.clear();
        mayNotBeOptimal = false;
        if (root != NULL)
                deleteTree(root, processEvents);
#ifdef QAPPLICATION_H
        if (!processEvents)
                QApplication::restoreOverrideCursor();
#endif
}

/*!
 * \brief Returns the sorted optimal path, starting from City 1.
 * \return A string, containing sorted optimal path.
 */
QString CTSPSolver::getSortedPath() const
{
        if (!root || route.isEmpty() || (route.size() != nCities))
                return QString();

int i = 0; // We start from City 1
QString path = tr("City %1").arg(1) + " -> ";
        while ((i = route[i]) != 0) {
                path += tr("City %1").arg(i + 1) + " -> ";
        }
        // And finish in City 1, too
        path += tr("City %1").arg(1);

        return path;
}

/*!
 * \brief Returns a total number of steps in the current solution.
 * \return A total number of steps or \c 0 if no solution.
 * \note This is not always the same as the number of cities.
 */
int CTSPSolver::getTotalSteps() const
{
        return total;
}

/*!
 * \brief Indicates whether or not the solution is definitely optimal.
 * \return \c true if the solution is definitely optimal, otherwise \c false.
 *
 *  The solution may need some further iterations to determine whether or not it is optimal.
 *  In such cases this function returns \c false.
 */
bool CTSPSolver::isOptimal() const
{
        return !mayNotBeOptimal;
}

/*!
 * \brief Solves the given task.
 * \param numCities Number of cities in the task.
 * \param task The matrix of city-to-city travel costs.
 * \return Pointer to the root of the solution tree.
 *
 * \todo TODO: Comment the algorithm.
 */
SStep *CTSPSolver::solve(int numCities, const TMatrix &task)
{
        if (numCities < 3)
                return NULL;

QMutexLocker locker(&mutex);
        cleanup();
        canceled = false;
        locker.unlock();

        nCities = numCities;

SStep *step = new SStep();
        step->matrix = task;
        // We need to distinguish the values forbidden by the user
        // from the values forbidden by the algorithm.
        // So we replace user's infinities by the maximum available double value.
        normalize(step->matrix);
#ifdef DEBUG
        qDebug() << step->matrix;
#endif // DEBUG
        step->price = align(step->matrix);
        root = step;

SStep *left, *right;
int nRow, nCol;
bool firstStep = true;
double check = INFINITY;
        total = 0;
        while (route.size() < nCities) {
                step->alts = findCandidate(step->matrix,nRow,nCol);

                while (hasSubCycles(nRow,nCol)) {
#ifdef DEBUG
                        qDebug() << "Forbidden: (" << nRow << ";" << nCol << ")";
#endif // DEBUG
                        step->matrix[nRow][nCol] = INFINITY;
                        step->price += align(step->matrix);
                        step->alts = findCandidate(step->matrix,nRow,nCol);
                }

#ifdef DEBUG
                qDebug() /*<< step->matrix*/ << "Selected: (" << nRow << ";" << nCol << ")";
                qDebug() << "Alternate:" << step->alts;
                qDebug() << "Step price:" << step->price << endl;
#endif // DEBUG

                locker.relock();
                if ((nRow == -1) || (nCol == -1) || canceled) {
                        cleanup();
                        return NULL;
                }
                locker.unlock();

                // Route with (nRow,nCol) path
                right = new SStep();
                right->pNode = step;
                right->matrix = step->matrix;
                for (int k = 0; k < nCities; k++) {
                        if (k != nCol)
                                right->matrix[nRow][k] = INFINITY;
                        if (k != nRow)
                                right->matrix[k][nCol] = INFINITY;
                }
                right->price = step->price + align(right->matrix);
                // Forbid the selected route to exclude its reuse in next steps.
                right->matrix[nCol][nRow] = INFINITY;
                right->matrix[nRow][nCol] = INFINITY;

                // Route without (nRow,nCol) path
                left = new SStep();
                left->pNode = step;
                left->matrix = step->matrix;
                left->matrix[nRow][nCol] = INFINITY;
                left->price = step->price + align(left->matrix);

                step->candidate.nRow = nRow;
                step->candidate.nCol = nCol;
                step->plNode = left;
                step->prNode = right;

                // This matrix is not used anymore. Restoring infinities back.
                denormalize(step->matrix);

                if (right->price <= left->price) {
                        // Route with (nRow,nCol) path is cheaper
                        step->next = SStep::RightBranch;
                        step = right;
                        route[nRow] = nCol;
                        emit routePartFound(route.size());
                        if (firstStep) {
                                check = left->price;
                                firstStep = false;
                        }
                } else {
                        // Route without (nRow,nCol) path is cheaper
                        step->next = SStep::LeftBranch;
                        step = left;
                        QCoreApplication::processEvents();
                        if (firstStep) {
                                check = right->price;
                                firstStep = false;
                        }
                }
                total++;
        }

        mayNotBeOptimal = (check < step->price);

        return root;
}

/*!
 * \brief Indicates whether or not the solution process was canceled.
 * \return \c true if the solution process was canceled, otherwise \c false.
 */
bool CTSPSolver::wasCanceled() const
{
QMutexLocker locker(&mutex);
        return canceled;
}

/*!
 * \brief Cancels the solution process.
 */
void CTSPSolver::cancel()
{
QMutexLocker locker(&mutex);
        canceled = true;
}

CTSPSolver::~CTSPSolver()
{
        if (root != NULL)
                deleteTree(root);
}

/* Privates **********************************************************/

double CTSPSolver::align(TMatrix &matrix)
{
double r = 0;
double min;
        for (int k = 0; k < nCities; k++) {
                min = findMinInRow(k,matrix);
                if (min > 0) {
                        r += min;
                        if (min < MAX_DOUBLE)
                                subRow(matrix,k,min);
                }
        }
        for (int k = 0; k < nCities; k++) {
                min = findMinInCol(k,matrix);
                if (min > 0) {
                        r += min;
                        if (min < MAX_DOUBLE)
                                subCol(matrix,k,min);
                }
        }
        return (r != MAX_DOUBLE) ? r : INFINITY;
}

void CTSPSolver::deleteTree(SStep *&root, bool processEvents)
{
        if (root == NULL)
                return;
SStep *step = root;
SStep *parent;
        forever {
                if (processEvents)
                        QCoreApplication::processEvents(QEventLoop::ExcludeUserInputEvents);
                if (step->plNode != NULL) {
                        // We have left child node - going inside it
                        step = step->plNode;
                        step->pNode->plNode = NULL;
                        continue;
                } else if (step->prNode != NULL) {
                        // We have right child node - going inside it
                        step = step->prNode;
                        step->pNode->prNode = NULL;
                        continue;
                } else {
                        // We have no child nodes. Deleting the current one.
                        parent = step->pNode;
                        delete step;
                        if (parent != NULL) {
                                // Going back to the parent node.
                                step = parent;
                        } else {
                                // We came back to the root node. Finishing.
                                root = NULL;
                                break;
                        }
                }
        }
}

void CTSPSolver::denormalize(TMatrix &matrix) const
{
        for (int r = 0; r < nCities; r++)
                for (int c = 0; c < nCities; c++)
                        if ((r != c) && (matrix.at(r).at(c) == MAX_DOUBLE))
                                matrix[r][c] = INFINITY;
}

QList<SStep::SCandidate> CTSPSolver::findCandidate(const TMatrix &matrix, int &nRow, int &nCol) const
{
        nRow = -1;
        nCol = -1;
QList<SStep::SCandidate> alts;
SStep::SCandidate cand;
double h = -1;
double sum;
        for (int r = 0; r < nCities; r++)
                for (int c = 0; c < nCities; c++)
                        if (matrix.at(r).at(c) == 0) {
                                sum = findMinInRow(r,matrix,c) + findMinInCol(c,matrix,r);
                                if (sum > h) {
                                        h = sum;
                                        nRow = r;
                                        nCol = c;
                                        alts.clear();
                                } else if ((sum == h) && !hasSubCycles(r,c)) {
                                        cand.nRow = r;
                                        cand.nCol = c;
                                        alts.append(cand);
                                }
                        }
        return alts;
}

double CTSPSolver::findMinInCol(int nCol, const TMatrix &matrix, int exr) const
{
double min = INFINITY;
        for (int k = 0; k < nCities; k++)
                if ((k != exr) && (min > matrix.at(k).at(nCol)))
                        min = matrix.at(k).at(nCol);
        return (min == INFINITY) ? 0 : min;
}

double CTSPSolver::findMinInRow(int nRow, const TMatrix &matrix, int exc) const
{
double min = INFINITY;
        for (int k = 0; k < nCities; k++) {
                if (((k != exc)) && (min > matrix.at(nRow).at(k)))
                        min = matrix.at(nRow).at(k);
        }
        return (min == INFINITY) ? 0 : min;
}

bool CTSPSolver::hasSubCycles(int nRow, int nCol) const
{
        if ((nRow < 0) || (nCol < 0) || route.isEmpty() || !(route.size() < nCities - 1) || !route.contains(nCol))
                return false;
int i = nCol;
        forever {
                if ((i = route.value(i)) == nRow)
                        return true;
                if (!route.contains(i))
                        return false;
        }
        return false;
}

void CTSPSolver::normalize(TMatrix &matrix) const
{
        for (int r = 0; r < nCities; r++)
                for (int c = 0; c < nCities; c++)
                        if ((r != c) && (matrix.at(r).at(c) == INFINITY))
                                matrix[r][c] = MAX_DOUBLE;
}

void CTSPSolver::subCol(TMatrix &matrix, int nCol, double val)
{
        for (int k = 0; k < nCities; k++)
                if (k != nCol)
                        matrix[k][nCol] -= val;
}

void CTSPSolver::subRow(TMatrix &matrix, int nRow, double val)
{
        for (int k = 0; k < nCities; k++)
                if (k != nRow)
                        matrix[nRow][k] -= val;
}

}

#ifdef DEBUG
QDebug operator<<(QDebug dbg, const TSPSolver::TMatrix &matrix)
{
        for (int r = 0; r < matrix.count(); r++) {
                for (int c = 0; c < matrix.at(r).count(); c++)
                        dbg.space() << QString::number(matrix.at(r).at(c)).leftJustified(5);
                dbg << endl;
        }
        return dbg;
}

QDebug operator<<(QDebug dbg, const TSPSolver::SStep::SCandidate &cand)
{
        dbg.nospace() << "(" << cand.nRow << ";" << cand.nCol << ")";
        return dbg;
}
#endif // DEBUG