HackerEarth Chocolates and Boxes problem solution

In this Leetcode 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


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;
}


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