Example: graphs_astar_example

Demo for the A* generic solver:

Example console output:

Input an integer number to solve a problem, or "e" to end.
761
An optimal solution has been found:
    2 coins of 2 piastres.
    0 coins of 7 piastres.
    2 coins of 8 piastres.
    39 coins of 19 piastres.

C++ example source code:

/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          https://www.mrpt.org/                         |
   |                                                                        |
   | Copyright (c) 2005-2024, Individual contributors, see AUTHORS file     |
   | See: https://www.mrpt.org/Authors - All rights reserved.               |
   | Released under BSD License. See: https://www.mrpt.org/License          |
   +------------------------------------------------------------------------+ */

#include <mrpt/graphs/CAStarAlgorithm.h>

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>

using namespace std;
using namespace mrpt::graphs;

class CCoinDistribution
{
   public:
    size_t coins2{0};
    size_t coins7{0};
    size_t coins8{0};
    size_t coins19{0};
    CCoinDistribution() {}
    size_t money() const
    {
        return 2 * coins2 + 7 * coins7 + 8 * coins8 + 19 * coins19;
    }
    inline bool operator==(const CCoinDistribution& mon) const
    {
        return (coins2 == mon.coins2) && (coins7 == mon.coins7) &&
            (coins8 == mon.coins8) && (coins19 == mon.coins19);
    }
};

class CAStarExample : public CAStarAlgorithm<CCoinDistribution>
{
   private:
    const size_t N;

   public:
    CAStarExample(size_t goal) : N(goal) {}
    bool isSolutionEnded(const CCoinDistribution& s) override
    {  // True if the solution is complete.
        return s.money() == N;
    }
    bool isSolutionValid(const CCoinDistribution& s) override
    {  // True if the solution is valid.
        return s.money() <= N;
    }
    void generateChildren(
        const CCoinDistribution& s, vector<CCoinDistribution>& sols) override
    {  // Get all the children of a solution.
        // Complex classes might want to define a copy constructor (note how the
        // vector in the following line is created by cloning this object four
        // times).
        sols = vector<CCoinDistribution>(4, s);
        sols[0].coins2++;  // Misma solución, más una moneda de 2.
        sols[1].coins7++;  // Misma solución, más una moneda de 7.
        sols[2].coins8++;  // Misma solución, más una moneda de 8...
        sols[3].coins19++;  // Y misma solución, más una moneda de 19.
    }
    double getHeuristic(const CCoinDistribution& s) override
    {  // Heuristic cost of the remaining part of the solution.
        // Check the documentation of CAStarAlgorithm to know which
        // characteristics does this function need to comply.
        return static_cast<double>(N - s.money()) / 19.0;
    }
    double getCost(const CCoinDistribution& s) override
    {  // Known cost of the partial solution.
        return s.coins2 + s.coins7 + s.coins8 + s.coins19;
    }
};

int main(int argc, char** argv)
{
    for (;;)
    {
        char text[11];
        printf(
            "Input an integer number to solve a problem, or \"e\" to end.\n");
        if (1 !=
            scanf(
                "%10s",
                text))  // GCC warning: scanf -> return cannot be ignored!
        {
            printf("Please, input a positive integer.\n\n");
            continue;
        }
        if (strlen(text) == 1 && (text[0] == 'e' || text[0] == 'E')) break;
        int val = atoi(text);
        if (val <= 0)
        {
            printf("Please, input a positive integer.\n\n");
            continue;
        }
        // The solution objects and the problem are created...
        CCoinDistribution solIni,
            solFin;  // Initial solution automatically initialized to (0,0,0,0).
        CAStarExample prob(static_cast<size_t>(val));
        switch (prob.getOptimalSolution(solIni, solFin, HUGE_VAL, 15))
        {
            case 0:
                printf(
                    "No solution has been found. Either the number is too "
                    "small, or the time elapsed has exceeded 15 seconds.\n\n");
                break;
            case 1:
                printf("An optimal solution has been found:\n");
                printf(
                    "\t%u coins of 2 piastres.\n\t%u coins of 7 "
                    "piastres.\n\t%u coins of 8 piastres.\n\t%u coins of 19 "
                    "piastres.\n\n",
                    (unsigned)solFin.coins2, (unsigned)solFin.coins7,
                    (unsigned)solFin.coins8, (unsigned)solFin.coins19);
                break;
            case 2:
                printf(
                    "A solution has been found, although it may not be "
                    "optimal:\n");
                printf(
                    "\t%u coins of 2 piastres.\n\t%u coins of 7 "
                    "piastres.\n\t%u coins of 8 piastres.\n\t%u coins of 19 "
                    "piastres.\n\n",
                    (unsigned)solFin.coins2, (unsigned)solFin.coins7,
                    (unsigned)solFin.coins8, (unsigned)solFin.coins19);
                break;
        }
    }
    return 0;
}