# include <cmath>
# include <cstdlib>
# include <iomanip>
# include <iostream>

using namespace std;

# include "tsp_nearest.hpp"

//****************************************************************************80

void tsp_nearest ( int n, double *x, int *order_best, double &cost_best )

//****************************************************************************80
//
//  Purpose:
//
//    tsp_nearest() seeks an optimal traveling salesperson path by the nearest neighbor method.
//
//  Licensing:
//
//    This code is distributed under the MIT license.
//
//  Modified:
//
//    14 July 2026
//
//  Author:
//
//    John Burkardt
//
//  Input:
//
//    int n: the number of cities.
//
//    double *x[n*2]: the coordinates of the cities.
//
//  Output:
//
//    int order_best[n]: the order in which the N cities should be visited.
//
//    double &cost_best: the length of the round trip.
//
{
  double cost;
  int i;
  int *order;
  int start;
//
//  Initialize:
//    the best cost so far is Infinity;
//    the best tour so far is 1, 2, ..., n.
//
  cost_best = HUGE_VAL;
  for ( i = 0; i < n; i++ )
  {
    order_best[i] = i;
  }
//
//  Try starting at city START and moving to nearest neighbor.
//
  for ( start = 0; start < n; start++ )
  {
    order = tsp_tour_nearest ( n, x, start );
    cost = tsp_tour_cost ( n, x, order );

    if ( cost < cost_best )
    {
      cout << "Order best:";
      for ( i = 0; i < n; i++ )
      {
        order_best[i] = order[i];
        cout << "  " << order_best[i];
      }
      cost_best = cost;
      cout << "  Route starting at city " << start
           << " has cost = " << cost_best << "\n";
      
    } 
    delete [] order;
  }

  return;
}
//****************************************************************************80

double tsp_tour_cost ( int n, double *x, int *order )

//****************************************************************************80
//
//  Purpose:
//
//    tsp_tour_cost() evaluates the cost of a round trip.
//
//  Licensing:
//
//    This code is distributed under the MIT license.
//
//  Modified:
//
//    19 July 2026
//
//  Author:
//
//    John Burkardt
//
//  Input:
//
//    int n: the number of cities.
//
//    double x[n,2]: the city locations.
//
//    int order[n]: the order in which cities are visited.
//
//  Output:
//
//    double cost: the cost of the route.
//
{
  double cost;
  int from;
  int to;

  cost = 0.0;
  from = n - 1;
  for ( to = 0; to < n; to++ )
  {
    cost = cost + sqrt ( pow ( x[order[from]*2]   - x[order[to]*2],   2 )
                       + pow ( x[order[from]*2+1] - x[order[to]*2+1], 2 ) );
    from = to;
  }

  return cost;
}
//****************************************************************************80

int *tsp_tour_nearest ( int n, double *x, int start )

//****************************************************************************80
//
//  Purpose:
//
//    tsp_tour_nearest() finds a nearest neighbor route for a given start.
//
//  Licensing:
//
//    This code is distributed under the MIT license.
//
//  Modified:
//
//    14 July 2026
//
//  Author:
//
//    John Burkardt
//
//  Input:
//
//    int n: the number of cities.
//
//    double x[n,2]: the city coordinates.
//
//    int start: the starting city.
//
//  Output:
//
//    int order[n]: the route that starts at START.
//
{
  double *d;
  double dmin;
  int from;
  int i;
  int j;
  int k;
  int *order;
  int to;
//
//  Make a copy of the distance table that we can modify.
//
  d = new double [n*n];

  for ( i = 0; i < n; i++ )
  {
    for ( j = 0; j < n; j++ )
    {
      d[i+j*n] = sqrt ( pow ( x[i*2]   - x[j*2],   2 )
                      + pow ( x[i*2+1] - x[j*2+1], 2 ) );

    }
  }
  for ( i = 0; i < n; i++ )
  {
    d[i+i*n] = HUGE_VAL;
  }
//
//  At FROM, find nearest unvisited city TO.
//
  order = new int[n];

  for ( j = 0; j < n; j++ )
  {
    if ( j == 0 )
    {
      to = start;
    }
    else
    {
      to = 0;
      dmin = d[from+to*n];
      for ( k = 1; k < n; k++ )
      {
        if ( d[from+k*n] < dmin )
        {
          to = k;
          dmin = d[from+to*n];
        }
      }
    }
//
//  Add TO to path, and move there.
//
    order[j] = to;
    from = to;
//
//  Reset D so we can't revisit city TO.
//
    for ( i = 0; i < n; i++ )
    {
      d[i+to*n] = HUGE_VAL;
    }
  }
  
  delete [] d;

  return order;
}