There is a special form for boolean formulas called "Conjunctive Normal Form" (CNF). A problem in this form consists of clauses connected with and operators, where each clause only contains variables connected with or operators. The variables can appear negated, but only variables can be directly negated, something like !(a && b) is not allowed. An example boolean formula in CNF form is:
return err("username cannot be empty");
。业内人士推荐新收录的资料作为进阶阅读
人 民 网 版 权 所 有 ，未 经 书 面 授 权 禁 止 使 用。新收录的资料是该领域的重要参考
# converts to prefix sum representation