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C++ Exercises: Count the Amicable pairs in an array

C++ Numbers: Exercise-29 with Solution

Write a program in C++ to count the Amicable pairs in an array.

Sample Solution:

C++ Code :

#include <bits/stdc++.h>
using namespace std;
 
int ProDivSum(int n)
{
    int sum = 1;
    for (int i=2; i<=sqrt(n); i++)
    {
        if (n%i == 0)
        {
            sum += i;
 
            // To handle perfect squares
            if (n/i != i)
                sum += n/i;
        }
    }
    return sum;
}
bool chkAmicable(int a,int b)
{
    return(ProDivSum(a) == b && ProDivSum(b) == a);
}
int ChkPairs(int arr[],int num1)
{
    int ctr = 0;
    for (int i=0; i<num1; i++)
        for (int j=i+1; j<num1; j++)
            if (chkAmicable(arr[i], arr[j]))
                ctr++;
    return ctr;
}
int main()
{
   int nn;
    int n, i, j, ctr;
 cout << "\n\n Count the Amicable pairs in a specific array: \n";
 cout << " Sample pairs : (220, 284)(1184,1210) (2620,2924) (5020,5564) (6232,6368)... \n";
 cout << " ------------------------------------------------------------------------------\n";
  cout << "\n Input the number of elements to be stored in the array: ";
       cin>>nn;
      int arr1[nn];
       for(i=0;i<nn;i++)
            {
	      cout<<"element - "<<i<<": ";
	      cin>>arr1[i];
	    }  
    int n1 = sizeof(arr1)/sizeof(arr1[0]);
    cout <<" Number of Amicable pairs presents in the array: "<< ChkPairs(arr1, n1) << endl;
    return 0;
}

Sample Output:

Count the Amicable pairs in a specific array:                         
 Sample pairs : (220, 284)(1184,1210) (2620,2924) (5020,5564) (6232,6368)...                                                                  
 ------------------------------------------------------------------------------                                                               
                                                                       
 Input the number of elements to be stored in the array: 2             
element - 0: 220                                                       
element - 1: 284                                                       
 Number of Amicable pairs presents in the array: 1 

Flowchart:

Flowchart: Count the amicable pairs in an array
Flowchart: Count the amicable pairs in an array
Flowchart: Count the amicable pairs in an array

C++ Code Editor:

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Next: Write a program in C++ to check if a given number is circular prime or not.

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C++ Programming: Tips of the Day

How to use the PI constant in C++?

On some (especially older) platforms (see the comments below) you might need to

#define _USE_MATH_DEFINES and then include the necessary header file:
#include<math.h>

and the value of pi can be accessed via:

M_PI

In math.h (2014) it is defined as:

# define M_PI           3.14159265358979323846  /* pi */

but check your math.h for more. An extract from the "old" math.h (in 2009):

/* Define _USE_MATH_DEFINES before including math.h to expose these macro
 * definitions for common math constants.  These are placed under an #ifdef 
 * since these commonly-defined names are not part of the C/C++ standards.
 */

However:

  1. on newer platforms (at least on my 64 bit Ubuntu 14.04) I do not need to define the _USE_MATH_DEFINES
  2. On (recent) Linux platforms there are long double values too provided as a GNU Extension:
# define M_PIl          3.14159265358979323846

Ref: https://bit.ly/3G4BgzQ