ECNUOJ 2574 Principles of Compiler

Principles of Compiler

Time Limit:1000MS Memory Limit:65536KB
Total Submit:473 Accepted:106

Description 

After learnt the Principles of Compiler,partychen thought that he can solve a simple expression problem.So he give you strings of less than 100 characters which strictly adhere to the following grammar (given in EBNF):
    A:= '(' B')'|'x'.
    B:=AC.
    C:={'+'A}.
Can you solve them too?

Input 

The first line of input gives the number of cases, N(1 ≤ N ≤ 100). N test cases follow.
The next N lines will each contain a string as described above.

Output 

For each test case,if the expression is adapt to the EBNF above output “Good”,else output “Bad”.

Sample Input 

3
(x)
(x+(x+x))
()(x)

Sample Output 

Good
Good
Bad

Source

解题：几十万只草泥马呼啸而过，一直没搞懂{+A}的含义

 

重复 { ... } 也就是说这个是表示+A可以出现0次或多次

 1 #include <bits/stdc++.h>

 2 using namespace std;

 3 const int maxn = 210;

 4 char str[maxn];

 5 int cur;

 6 bool A();

 7 bool B();

 8 bool C();

 9 bool A() {

10     if(str[cur] == 'x') {

11         cur++;

12         return true;

13     }

14      if(str[cur] == '(') {

15         cur++;

16         if(B() && str[cur] == ')') {

17             cur++;

18             return true;

19         }

20     }

21     return false;

22 }

23 bool B() {

24     return A() && C();

25 }

26 bool C() {

27     while(str[cur] == '+'){

28         cur++;

29         if(!A()) return false;

30     }

31     return true;

32 }

33 int main() {

34     int kase;

35     scanf("%d",&kase);

36     getchar();

37     while(kase--) {

38         gets(str);

39         cur = 0;

40         puts(A() && str[cur] == '\0'?"Good":"Bad");

41     }

42     return 0;

43 }

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