编译原理紫龙书(Compilers:Principles,Techniques and Tools Second Edition)部分答案

3.3.2 : Describe the languages denoted by the following regular expressions:

2: 所有的由a和b组成的串。

3: This regular expression denotes the language that takes zero or many instances of “a” or “b” as the prefix, followed with an “a”, ended with a string in{aa,ab,ba,bb}.

3.3.5

6 All strings of a's and b's with an even number of a's and an odd number of b's.

 even_a_even_b →（aa|bb）*  ((ab|ba)(aa|bb)*(ab|ba)(aa|bb)*)*

even_a_odd_b→ b even_a_even_b  |  a (aa|bb)*(ab|ba) even_a_even_b

 

对于偶数个a和奇数个b构成的串，其第一个字符可能是a或b

（1）如果是b，那么剩下的部分一定是偶数个a和偶数个b

（2）如果是a，那么经过若干个aa或bb，一定会出现一个ab或ba，才能保证a的个数是偶数，b的个数是奇数。若串还没有结束，剩余部分一定是偶数个a和偶数个b

 

8 （b*a* | b* | a*)(aa*b)*a*  |  (b*a*|b*|a*)(ba*a)*(a*|b)      

9:  b^*a^* ba^*  | b^* a^*

 

 

3.5.2

%{

           FILE * fp  = fopen(“copyfile”,”w”);

%}

           non_whitespace [ASCII or characters expect blank, tab and newline]

           whitespace    [ blank and /t/n]

%%

           {whitespace}+  {fprint(fp,%c,’  ‘);}

           {non_whitespace}   {fprint(fp,%c,yytext[0]);}

 

3.6.5

1:

State

a

b

e

0

{0,1}

{0}

￠

1

{1,2}

{1}

￠

2

{2}

{2,3}

{0}

3

￠

￠

￠