Fast-Fourier-Transform-FFT Hàm sinh - Đa thức - Nhân đa thức Cơ sở lý thuyết Codeforces: https://codeforces.com/blog/entry/43499 CP Algorithms: https://cp-algorithms.com/algebra/fft.html Art of Problem Solving: https://artofproblemsolving.com/wiki/index.php/Polynomial Exercises Part 1: https://codeforces.com/blog/entry/77468 Part 2: https://codeforces.com/blog/entry/77551