Doubt regading NTT

I have a doubt about how devide polynomial in NTT.Specifically in this problem
link :
In editorial and many solution,they are deviding polynomial into 3 polynomials.
I didn’t understand why 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.

Sorry bro,its very sad that no pro coder is there now to help us(Beginners)…this is responsibility of author to clear ur all genuine doubts.

@admin please help us

You should ask your doubts in the editorial page