I have a doubt about how devide polynomial in NTT.Specifically in this problem link :https://www.codechef.com/JULY16/problems/POLYEVAL/ In editorial and many solution,they are deviding polynomial into 3 polynomials as A(x^3)+xA(x^3)+x^2A(x^3). I didn't understand why it is needed to devide the polynomial into 3 polynomial first and then apply NTT. Can we take whole polynomial into single array and do it's NTT.Please Clarify my doubt.