查看正则表达式重复是否可以减少的算法

Question

我正在寻找一种算法,可以检查嵌套的正则表达式重复是否可以减少.假设解析正则表达式已经完成.

例:

(1{1,2}){1,2} === 1{1,4}
    It matches 1, 11, 111, 1111 which can be rewritten as a single repeat

(1{2,2}){1,2} can not be reduced
    It matches 11 and 1111 which can not be rewritten as a single repeat.

(1{10,11}){1,2} can not be reduced

(1{10,19}){1,2} === 1{10,38}

(1{1,2}){10,11} === 1{10,22}

(1{10,11})* can not be reduced

(1*){10,11} === 1*

我一直试图找到这种类型的操作模式,而不必匹配所有可能的解决方案,并寻找可以防止它被减少的漏洞.必须有一个简单的函数(f( A, B, C, D ) -> ( E, F ))可以解决任意输入,如下所示:

(1{A,B}){C,D} -> 1{E,F}

Answer 1

// (x{A,B}){C,D} -> x{E,F}
bool SimplifyNestedRepetition(int A, int B,
                              int C, int D,
                              out int E, out int F)
{
    if (B == -1 || C == D || A*(C+1) <= B*C + 1)
    {
        E = A*C;

        if (B == -1 || D == -1) F = -1;
        else F = B*D;

        return true;
    }
    return false;
}

• 如果x{A,B}无限制，则可以重复任意次数。
• (x{A,B}){C}总是可还原的。
• 如果，您可以减少它，因为最长的重复序列和最短的重复序列A*(C+1) <= B*C + 1之间没有间隙。CC+1

B = -1orD == -1表示无限，如x*or x{5,}。

测试用例：

Input           Reducible?
(x{0,0}){0,0}   Yes - x{0,0}
(x{0,1}){0,0}   Yes - x{0,0}
(x{0,2}){0,0}   Yes - x{0,0}
(x{1,1}){0,0}   Yes - x{0,0}
(x{1,2}){0,0}   Yes - x{0,0}
(x{1,3}){0,0}   Yes - x{0,0}
(x{2,2}){0,0}   Yes - x{0,0}
(x{2,3}){0,0}   Yes - x{0,0}
(x{2,4}){0,0}   Yes - x{0,0}
(x{0,0}){0,1}   Yes - x{0,0}
(x{0,1}){0,1}   Yes - x{0,1}
(x{0,2}){0,1}   Yes - x{0,2}
(x{1,1}){0,1}   Yes - x{0,1}
(x{1,2}){0,1}   Yes - x{0,2}
(x{1,3}){0,1}   Yes - x{0,3}
(x{2,2}){0,1}   No 
(x{2,3}){0,1}   No 
(x{2,4}){0,1}   No 
(x{0,0}){0,2}   Yes - x{0,0}
(x{0,1}){0,2}   Yes - x{0,2}
(x{0,2}){0,2}   Yes - x{0,4}
(x{1,1}){0,2}   Yes - x{0,2}
(x{1,2}){0,2}   Yes - x{0,4}
(x{1,3}){0,2}   Yes - x{0,6}
(x{2,2}){0,2}   No 
(x{2,3}){0,2}   No 
(x{2,4}){0,2}   No 
(x{0,0}){1,1}   Yes - x{0,0}
(x{0,1}){1,1}   Yes - x{0,1}
(x{0,2}){1,1}   Yes - x{0,2}
(x{1,1}){1,1}   Yes - x{1,1}
(x{1,2}){1,1}   Yes - x{1,2}
(x{1,3}){1,1}   Yes - x{1,3}
(x{2,2}){1,1}   Yes - x{2,2}
(x{2,3}){1,1}   Yes - x{2,3}
(x{2,4}){1,1}   Yes - x{2,4}
(x{0,0}){1,2}   Yes - x{0,0}
(x{0,1}){1,2}   Yes - x{0,2}
(x{0,2}){1,2}   Yes - x{0,4}
(x{1,1}){1,2}   Yes - x{1,2}
(x{1,2}){1,2}   Yes - x{1,4}
(x{1,3}){1,2}   Yes - x{1,6}
(x{2,2}){1,2}   No 
(x{2,3}){1,2}   Yes - x{2,6}
(x{2,4}){1,2}   Yes - x{2,8}
(x{0,0}){1,3}   Yes - x{0,0}
(x{0,1}){1,3}   Yes - x{0,3}
(x{0,2}){1,3}   Yes - x{0,6}
(x{1,1}){1,3}   Yes - x{1,3}
(x{1,2}){1,3}   Yes - x{1,6}
(x{1,3}){1,3}   Yes - x{1,9}
(x{2,2}){1,3}   No 
(x{2,3}){1,3}   Yes - x{2,9}
(x{2,4}){1,3}   Yes - x{2,12}
(x{0,0}){2,2}   Yes - x{0,0}
(x{0,1}){2,2}   Yes - x{0,2}
(x{0,2}){2,2}   Yes - x{0,4}
(x{1,1}){2,2}   Yes - x{2,2}
(x{1,2}){2,2}   Yes - x{2,4}
(x{1,3}){2,2}   Yes - x{2,6}
(x{2,2}){2,2}   Yes - x{4,4}
(x{2,3}){2,2}   Yes - x{4,6}
(x{2,4}){2,2}   Yes - x{4,8}
(x{0,0}){2,3}   Yes - x{0,0}
(x{0,1}){2,3}   Yes - x{0,3}
(x{0,2}){2,3}   Yes - x{0,6}
(x{1,1}){2,3}   Yes - x{2,3}
(x{1,2}){2,3}   Yes - x{2,6}
(x{1,3}){2,3}   Yes - x{2,9}
(x{2,2}){2,3}   No 
(x{2,3}){2,3}   Yes - x{4,9}
(x{2,4}){2,3}   Yes - x{4,12}
(x{0,0}){2,4}   Yes - x{0,0}
(x{0,1}){2,4}   Yes - x{0,4}
(x{0,2}){2,4}   Yes - x{0,8}
(x{1,1}){2,4}   Yes - x{2,4}
(x{1,2}){2,4}   Yes - x{2,8}
(x{1,3}){2,4}   Yes - x{2,12}
(x{2,2}){2,4}   No 
(x{2,3}){2,4}   Yes - x{4,12}
(x{2,4}){2,4}   Yes - x{4,16}