M.O.Rabin
Rabin-Karp算法，是由M.O.Rabin和R.A.Karp设计实现的一种基于移动散列值的字符串匹配算法。
通常基于散列值的字符串匹配方法：（1）首先计算模式字符串的散列函数；（2）然后利用相同的散列函数计算文本中所有可能的M个字符的子字符串的散列函数值并寻找匹配。但是这种方法比暴力查找还慢，因为计算散列值会涉及字符串中的每个字符。Rabin和Karp对上述方法进行了改进，设计实现了一种能够在常数时间内算出M个字符的子字符串散列值的方法。
运行效果：
源代码：
using System;
using System.Text;
using System.Collections;
using System.Collections.Generic;
namespace Legalsoft.Truffer.Algorithm
{
public static partial class PatternSearch
{
public readonly static int ALPHA_CODE_MAX = 256;
/// <summary>
/// 字符串匹配算法（模式搜索）Rabin Karp 算法
/// </summary>
/// <param name="text"></param>
/// <param name="pattern"></param>
/// <param name="primeNumber"></param>
/// <returns></returns>
public static List<int> Rabin_Karp_Search( string text,string pattern, int primeNumber = 101)
{
List<int> matchs = new List<int>();
int M = pattern.Length;
int N = text.Length;
int h = 1;
for (int i = 0; i < M - 1; i++)
{
h = (h * ALPHA_CODE_MAX) % primeNumber;
}
int p = 0;
int t = 0;
for (int i = 0; i < M; i++)
{
p = (ALPHA_CODE_MAX * p + pattern[i]) % primeNumber;
t = (ALPHA_CODE_MAX * t + text[i]) % primeNumber;
}
for (int i = 0; i <= N - M; i++)
{
if (p == t)
{
int j;
for (j = 0; j < M; j++)
{
if (text[i + j] != pattern[j])
{
break;
}
}
if (j == M)
{
matchs.Add(i);
}
}
if (i < (N - M))
{
t = (ALPHA_CODE_MAX * (t - text[i] * h) + text[i + M]) % primeNumber;
if (t < 0)
{
t = (t + primeNumber);
}
}
}
return matchs;
}
}
}
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POWER BY TRUFFER.CN
using System;
using System.Text;
using System.Collections;
using System.Collections.Generic;namespace Legalsoft.Truffer.Algorithm
{public static partial class PatternSearch{public readonly static int ALPHA_CODE_MAX = 256;/// <summary>/// 字符串匹配算法（模式搜索）Rabin Karp 算法/// </summary>/// <param name="text"></param>/// <param name="pattern"></param>/// <param name="primeNumber"></param>/// <returns></returns>public static List<int> Rabin_Karp_Search( string text,string pattern, int primeNumber = 101){List<int> matchs = new List<int>();int M = pattern.Length;int N = text.Length;int h = 1;for (int i = 0; i < M - 1; i++){h = (h * ALPHA_CODE_MAX) % primeNumber;}int p = 0;int t = 0;for (int i = 0; i < M; i++){p = (ALPHA_CODE_MAX * p + pattern[i]) % primeNumber;t = (ALPHA_CODE_MAX * t + text[i]) % primeNumber;}for (int i = 0; i <= N - M; i++){if (p == t){int j;for (j = 0; j < M; j++){if (text[i + j] != pattern[j]){break;}}if (j == M){matchs.Add(i);}}if (i < (N - M)){t = (ALPHA_CODE_MAX * (t - text[i] * h) + text[i + M]) % primeNumber;if (t < 0){t = (t + primeNumber);}}}return matchs;}}
}
