//+------------------------------------------------------------------+
//|                                            demo_combinations.mq5 |
//|                                        Copyright © 2018, Amr Ali |
//|                             https://www.mql5.com/en/users/amrali |
//+------------------------------------------------------------------+
#property copyright "Copyright © 2018, Amr Ali"
#property link      "https://www.mql5.com/en/users/amrali"
#property version   "1.000"
#property description "A demo for combinations in MQL."
#property strict
#property script_show_inputs

#include <Permut_library.mqh>

sinput string s; //different ways to choose a committee of K out of N candidates

input int N = 5;
input int K = 3;
//+------------------------------------------------------------------+
//|                                                                  |
//+------------------------------------------------------------------+
/**
 * Convert the input array into a string and returns the result.
 * The returned string will separate the elements in the array
 * with commas like "[1,5,3,4]".
 */
template<typename T>
string arrayToString(const T &arr[])
  {
   int size=ArraySize(arr);
   if(!size) return "[]";
   string str= "["+(string)arr[0];
   for(int i = 1; i<size;++i)
      str+=", "+(string)arr[i];
   str+="]";
   return (str);
  }
//+------------------------------------------------------------------+
//|                                                                  |
//+------------------------------------------------------------------+
void OnStart()
  {
// dynamically allocate and intialize the candidates array
   int candidates[];

   ArrayResize(candidates,N);

   for(int i=0; i<N; i++)
     {
      candidates[i]=i+1;
     }

   printf("The candidates array: %s",arrayToString(candidates));

   printf("The possible combinations of %i persons chosen from %i should be: %I64i",K,N,nCk(N,K));
// 5C3 = 5 * 4 * 3 / (3 * 2 * 1) = 10

// store number of combinations generated
   int counter=0;

// array to receive combinations one by one
   int result[];

// choose "k out of n items"
   CombinationsIterator<int>comboIt(candidates,K,result);

   do
     {
      // output this combination
      printf("%i: %s",counter++,arrayToString(result));

     }
   while(comboIt.next(result));

  }
//+------------------------------------------------------------------+

/* sample output
 combinations_demo (GBPUSD,M1)	The candidates array: [1, 2, 3, 4, 5]
 combinations_demo (GBPUSD,M1)	The possible combinations of 3 persons chosen from 5 should be: 10
 combinations_demo (GBPUSD,M1)	0: [1, 2, 3]
 combinations_demo (GBPUSD,M1)	1: [1, 2, 4]
 combinations_demo (GBPUSD,M1)	2: [1, 2, 5]
 combinations_demo (GBPUSD,M1)	3: [1, 3, 4]
 combinations_demo (GBPUSD,M1)	4: [1, 3, 5]
 combinations_demo (GBPUSD,M1)	5: [1, 4, 5]
 combinations_demo (GBPUSD,M1)	6: [2, 3, 4]
 combinations_demo (GBPUSD,M1)	7: [2, 3, 5]
 combinations_demo (GBPUSD,M1)	8: [2, 4, 5]
 combinations_demo (GBPUSD,M1)	9: [3, 4, 5]
*/