用于模式搜索的 KMP 算法的 C# 程序
给定一个文本txt[0..n-1]和一个模式pat[0..m-1] ,编写一个函数search(char pat[], char txt[])打印txt中所有出现的pat[] [] 。您可以假设n > m 。
例子:
输入:txt[] = "THIS IS A TEST TEXT" pat[] = "TEST" 输出:在索引 10 找到的模式 输入:txt[] = "AABAACAADAABAABA" pat[] = "AABA" 输出:在索引 0 找到的模式在索引 9 找到的模式 在索引 12 找到的模式
模式搜索是计算机科学中的一个重要问题。当我们在记事本/word 文件或浏览器或数据库中搜索字符串时,会使用模式搜索算法来显示搜索结果。
C#
// C# program for implementation of KMP pattern
// searching algorithm
using System;
class GFG {
void KMPSearch(string pat, string txt)
{
int M = pat.Length;
int N = txt.Length;
// create lps[] that will hold the longest
// prefix suffix values for pattern
int[] lps = new int[M];
int j = 0; // index for pat[]
// Preprocess the pattern (calculate lps[]
// array)
computeLPSArray(pat, M, lps);
int i = 0; // index for txt[]
while (i < N) {
if (pat[j] == txt[i]) {
j++;
i++;
}
if (j == M) {
Console.Write("Found pattern "
+ "at index " + (i - j));
j = lps[j - 1];
}
// mismatch after j matches
else if (i < N && pat[j] != txt[i]) {
// Do not match lps[0..lps[j-1]] characters,
// they will match anyway
if (j != 0)
j = lps[j - 1];
else
i = i + 1;
}
}
}
void computeLPSArray(string pat, int M, int[] lps)
{
// length of the previous longest prefix suffix
int len = 0;
int i = 1;
lps[0] = 0; // lps[0] is always 0
// the loop calculates lps[i] for i = 1 to M-1
while (i < M) {
if (pat[i] == pat[len]) {
len++;
lps[i] = len;
i++;
}
else // (pat[i] != pat[len])
{
// This is tricky. Consider the example.
// AAACAAAA and i = 7. The idea is similar
// to search step.
if (len != 0) {
len = lps[len - 1];
// Also, note that we do not increment
// i here
}
else // if (len == 0)
{
lps[i] = len;
i++;
}
}
}
}
// Driver program to test above function
public static void Main()
{
string txt = "ABABDABACDABABCABAB";
string pat = "ABABCABAB";
new GFG().KMPSearch(pat, txt);
}
}
// This code has been contributed by Amit Khandelwal.
输出:
Found pattern at index 10
有关更多详细信息,请参阅关于模式搜索的 KMP 算法的完整文章!