Rabin-Karp 滚动哈希字符串匹配算法

Question

这是 Rabin-Karp 字符串匹配算法在 C# 中的实现...

static void Main(string[] args)
{
  string A = "String that contains a pattern.";
  string B = "pattern";
  ulong siga = 0;
  ulong sigb = 0;
  ulong Q = 100007;
  ulong D = 256;
for (int i = 0; i < B.Length; i++)
{
    siga = (siga * D + (ulong)A[i]) % Q;
    sigb = (sigb * D + (ulong)B[i]) % Q;
}
if (siga == sigb)
{
    Console.WriteLine(string.Format(">>{0}<<{1}", A.Substring(0, B.Length), A.Substring(B.Length)));
    return;
}
ulong pow = 1;
for (int k = 1; k <= B.Length - 1; k++)
    pow = (pow * D) % Q;

for (int j = 1; j <= A.Length - B.Length; j++)
{
    siga = (siga + Q - pow * (ulong)A[j - 1] %Q) % Q;
    siga = (siga * D + (ulong)A[j + B.Length - 1]) % Q;
    if (siga == sigb)
    {
        if (A.Substring(j, B.Length) == B)
        {
            Console.WriteLine(string.Format("{0}>>{1}<<{2}", A.Substring(0, j), 
                                                             A.Substring(j, B.Length), 
                                                             A.Substring(j +B.Length)));
            return;
        }
    }
}
Console.WriteLine("Not copied!");

}

但是如果我更改第二个字符串的位置，它会出现一个问题，它显示结果未复制，但

 string A = "String that contains a pattern.";
 string B = "pattern";

这里显示未复制

 string A = "String that contains a pattern.";
 string B = "Matches contains a pattern ";

我想检查它是否是复制从第一个字符串开始，甚至我会在其中添加一些内容或更改位置，但它应该没有什么区别，所以如何更改它，它只是比较字符串中每个单词的哈希值而不是实现它...... ......

Answer 1

更改

string B = "Matches contains a pattern ";

为

string B = "contains a pattern ";

，它将起作用