P3803 【模板】多项式乘法（FFT）

用到了python的第三方模块sympy

import sympy
#FFT
print(input()*0+' '.join(map(str,sympy.ifft(((c:=sympy.fft((a:=list(map(int,input().split())))+[0]*len(b:=list(map(int,input().split()))))),(d:=sympy.fft(b+[0]*len(a))),[i*j for i,j in zip(c,d)])[2])[:len(a)+len(b)-1])))

#NTT
print(input()*0+' '.join(map(str,sympy.intt(((c:=sympy.ntt((a:=list(map(int,input().split())))+[0]*len(b:=list(map(int,input().split()))),998244353)),(d:=sympy.ntt(b+[0]*len(a),998244353)),[i*j%998244353 for i,j in zip(c,d)])[2],998244353)[:len(a)+len(b)-1])))

不过洛谷不让用sympy啊...