Score : 800 points
Let’s take a prime P = 200\,003. You are given N integers A_1, A_2, \ldots, A_N. Find the sum of ((A_i \cdot A_j) \bmod P) over all N \cdot (N-1) / 2 unordered pairs of elements (i < j).
Please note that the sum isn't computed modulo P.
Input is given from Standard Input in the following format.
N A_1 A_2 \cdots A_N
Print one integer — the sum over ((A_i \cdot A_j) \bmod P).
4 2019 0 2020 200002
474287
The non-zero products are:
So the answer is 0 + 78320 + 197984 + 0 + 0 + 197983 = 474287.
5 1 1 2 2 100000
600013