Non-Divisible Subset

//https://www.hackerrank.com/challenges/non-divisible-subset/problem

#include <iostream>

using namespace std;

int main()
{
    long int c;
    int n,k,t,i,a[101]={0},s=0;
    cin>>n>>k;
    for(i=0;i<n;i++)
    {
        cin>>c;
        t=c%k;
        //we can directly store the remainders as 
        //were r intrested only in total elements
        // and store its frequency in an array
        a[t]++;
    }
    // if there there is 0, we can add it also, but not twice
    //as (0+0)/k=0(evenly divides). hence we take it only once.
    //NOTE: there is no k value as we are taking only remainder
    if(a[0]>=1)
        s=1;
    for(i=1;i<=k/2;i++)
    {
       // we shouldn't have any 2 numbers a, b so that a+b=k
       // so store only freq of either i or i-k , which is greater
       // but for i=k/2 , we can take frequency as one only cos
       // 2* (k/2)=k.
        if(a[i]==a[k-i]&&a[i]>=1)
            s+=1;
        else if(a[i]>a[k-i])
            s+=a[i];
        else
            s+=a[k-i];
        //cout<<s<<" "<<i<<endl;
    }
    cout<<s;    
    return 0;
}