设$ans=\sum\limits_{A \cap B=\varnothing} f(A)g(B) $
Direct enumeration subset violence $ O (3 ^ n) $, a first pre-processing technique is a $ h (S) = \ sum \ limits_ {T \ subseteq S} g (T) $
然后$ans=\sum\limits_{S\subseteq 2^{U}} f(S)g(2^{u}\backslash S)$
Such complexity is $ (n2 ^ n) O $