Problem A: Let P₀[i] = count of numbers i in array. P_k = P_k - 1 × P₀, where  ×  is multiplication of polynomials with AND applied to indices instead of sum (like it's described here, I don't know how to correctly name such multiplication). So the task is to find least k such that P_k[0] > 0, and answer will be P_k[0]·k!
It can be done in , where N = 2²⁰ , because k is limited by , and we can find P_k[0] in linear time, without inverse transformation.

Any simple approach for B? We tried and got TL 52.

H ?