M→HM' M'→aHM'|ε H→bH'|(M) H'→(M)|ε
是LL(1)文法 first(a)={b,ε} first(b)={a,b} follow(a)={b,#} follow(b)={b,#} 参考 https://blog.csdn.net/qq_43543789/article/details/105457051