count triplets with sum less than x

long long countTriplets(long long arr[], int n, long long sum)
	{
	    sort(arr, arr+n);
	    long long ans = 0;
	    for (int i = 0; i < n - 2; i++)
	    {
	        int j = i + 1, k = n - 1;
	        while (j < k)
	        {
	            if (arr[i] + arr[j] + arr[k] >= sum)
	                k--;
	            else
	            {
	                ans += (k - j);
	                j++;
	            }
	        }
	    }
	    return ans;
	}