I thought for a long time and tried something like FFT to solve it but failed.
In fact,I haven't find a algorithm better than brute force,which is $$$O(n^2)$$$.
Is there a better way to calculate it?
I thought for a long time and tried something like FFT to solve it but failed.
In fact,I haven't find a algorithm better than brute force,which is $$$O(n^2)$$$.