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;
}