给定一个上下文无关文法，根据算法设计一个程序，求文法中每个非终结符的 FirstVT 集和LastVT 集。依据文法和求出的相应FirstVT和 LastVT 集生成算符优先分析表。-Given a context-free grammar, algorithm design a program, find a grammar for each nonterminal the FirstVT the set and LastVT set. The basis the generated oper