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

#include <bits/stdc++.h>
using namespace std;
const int maxn = 210;
char str[maxn];
int cur;
bool A();
bool B();
bool C();
bool A() {
    if(str[cur] == 'x') {
        cur++;
        return true;
    }
     if(str[cur] == '(') {
        cur++;
        if(B() && str[cur] == ')') {
            cur++;
            return true;
        }
    }
    return false;
}
bool B() {
    return A() && C();
}
bool C() {
    while(str[cur] == '+'){
        cur++;
        if(!A()) return false;
    }
    return true;
}
int main() {
    int kase;
    scanf("%d",&kase);
    getchar();
    while(kase--) {
        gets(str);
        cur = 0;
        puts(A() && str[cur] == ''?"Good":"Bad");
    }
    return 0;
}