C Exercises: Count the amicable pairs in an array

Last update on March 19 2025 12:39:12 (UTC/GMT +8 hours)

26. Count Amicable Pairs in Array Variants

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

Sample Solution:

C Code:

# include <stdio.h>
# include <stdlib.h>
# include <stdbool.h>
# include <math.h>

// Function to find the sum of proper divisors of a number 'n'
int ProDivSum(int n)
{
    int sum = 1;
    for (int i = 2; i <= sqrt(n); i++) // Loop to find divisors of 'n'
    {
        if (n % i == 0)
        {
            sum += i; // Adding divisor 'i' to the sum
            if (n / i != i)
                sum += n / i; // Adding the corresponding divisor to the sum
        }
    }
    return sum; // Returning the sum of divisors
}

// Function to check if two numbers 'a' and 'b' are Amicable pairs
bool chkAmicable(int a, int b)
{
    return (ProDivSum(a) == b && ProDivSum(b) == a); // Checking if the sums of divisors of 'a' and 'b' match each other
}

// Function to count the number of Amicable pairs in an array
int ChkPairs(int arr[], int num1)
{
    int ctr = 0;
    for (int i = 0; i < num1; i++) // Loop through the elements of the array
    {
        for (int j = i + 1; j < num1; j++) // Loop through subsequent elements in the array
        {
            if (chkAmicable(arr[i], arr[j])) // Checking if the pair (arr[i], arr[j]) is an Amicable pair
                ctr++; // Incrementing the counter if an Amicable pair is found
        }
    }
    return ctr; // Returning the count of Amicable pairs
}

// Main function
int main()
{
    int nn; // Variable to store the number of elements in the array

    // Printing information about the program and asking for user input
    printf("\n\n Count the Amicable pairs in a specific array: \n");
    printf(" Sample pairs : (220, 284)(1184,1210) (2620,2924) (5020,5564) (6232,6368)... \n");
    printf(" ------------------------------------------------------------------------------\n");
    printf("\n Input the number of elements to be stored in the array: ");
    scanf("%d", &nn);

    int arr1[nn]; // Array to store elements entered by the user

    // Taking input of elements to be stored in the array
    for (int i = 0; i < nn; i++)
    {
        printf(" element - %d: ", i);
        scanf("%d", &arr1[i]);
    }

    int n1 = sizeof(arr1) / sizeof(arr1[0]); // Calculating the number of elements in the array

    // Displaying the number of Amicable pairs present in the array
    printf(" Number of Amicable pairs presents in the array: %d\n", ChkPairs(arr1, n1));

    return 0; // Returning 0 to indicate successful execution
}

Sample Output:

 Input the number of elements to be stored in the array: 4                                                    
 element - 0: 220                                                                                             
 element - 1: 274                                                                                             
 element - 2: 1184                                                                                            
 element - 3: 1210                                                                                            
 Number of Amicable pairs presents in the array: 1

Flowchart:

For more Practice: Solve these Related Problems:

• Write a C program to count amicable pairs in an array and list each pair with divisor details.
• Write a C program to optimize the search for amicable pairs using precomputed divisor sum arrays.
• Write a C program to implement amicable pair detection in an unsorted array with efficient lookups.
• Write a C program to count and display the index positions of amicable pairs found in an array.

C Programming Code Editor:

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