HackerEarth Modulo Strength problem solution

In this HackerEarth Modulo Strength problem solution Alice is the teacher of a class having N students, where each student is having some personality value, given in the form of an array A. Here Ai denotes the personality value of ith student, where 1 <= i <= N. Alice has a special integer K with her. Student i is a friend of Student j, if and only if (A[i] % K) = (A[j] % K). Each student’s strength is equal to the number of friends he/she has. Alice needs to calculate the sum of the strength of all the students in the class. Help Alice for the same.

#include<stdio.h>

int main()

{

int n,k;

long long int *arr,strength=0,*res;

scanf("%d",&n);

scanf("%d",&k);
 

arr = (long long int *) malloc( n * sizeof(long long int ));

res = (long long int *) malloc( k * sizeof( long long int ));

for(int i = 0 ; i<n ; i++)

{

scanf("%lld",&arr[i]);

}


for(int i = 0 ; i< n ; i++)

{

int loc = arr[i] % k;

res[loc] = res[loc] + 1;

}

 
for(int i = 0 ; i<k ; i++ )

{

if(res[i] == 0 || res[i] == 1)

continue;

strength = strength + ( res[i] * (res[i] - 1) ) ;

}


printf("%lld",strength);

  return 0;

}