Score: 500 points
We have caught N sardines. The deliciousness and fragrantness of the i-th sardine is A_i and B_i, respectively.
We will choose one or more of these sardines and put them into a cooler. However, two sardines on bad terms cannot be chosen at the same time.
The i-th and j-th sardines (i \neq j) are on bad terms if and only if A_i \cdot A_j + B_i \cdot B_j = 0.
In how many ways can we choose the set of sardines to put into the cooler? Since the count can be enormous, print it modulo 1000000007.
Input is given from Standard Input in the following format:
N A_1 B_1 : A_N B_N
Print the count modulo 1000000007.
3 1 2 -1 1 2 -1
5
There are five ways to choose the set of sardines, as follows:
10 3 2 3 2 -1 1 2 -1 -3 -9 -8 12 7 7 8 1 8 2 8 4
479