# HackerEarth Chocolates and Boxes problem solution

In this HackerEarth Chocolates and Boxes, problem-solution Alice has N boxes, and each box has a certain non-zero number of chocolates. These boxes are numbered from 1 to N.

Alice is planning to go to wonderland. She wants to carry exactly K number of chocolates and she can carry only 2 boxes. So she wants to know the number of ways in which she can select 2 boxes such that the total number of chocolates in them is K.

## HackerEarth Chocolates and Boxes problem solution.

`int main(){    int t;    cin>>t;    while(t--)    {        int n;        cin>>n;        int arr[300000];        rep(i,n)            cin>>arr[i];        int k;        cin>>k;        int mul[300000];        for(int i=0;i<k;i++)            mul[i]=0;        long long int ways=0;        for(int i=0;i<n;i++)        {            if(arr[i]<k)                mul[arr[i]%k]++;        }        for(int i=1;i<=(k/2);i++)        {            if(2*i == k && mul[i]>=2)                ways+=(mul[i]*(mul[i]-1)/2);            else                ways+=mul[i]*mul[k-i];        }        cout<<ways<<endl;    }    return 0;}`