用于模式搜索的KMP算法的C程序

给定文本txt [0..n-1]和模式pat [0..m-1] ，编写一个函数search(char pat []，char txt []) ，将所有出现的pat []都打印在txt中[] 。您可以假设n> m 。

例子：

输入：txt [] =“这是一个测试文本” pat [] =“ TEST”输出：在索引10处找到的模式输入：txt [] =“ AABAACAADAABAABA” pat [] =“ AABA”输出：在索引0处找到的模式在索引9处找到的模式在索引12处找到的模式

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/单词文件或浏览器或数据库中搜索字符串时，将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
#include 
  
void computeLPSArray(char* pat, int M, int* lps);
  
// Prints occurrences of txt[] in pat[]
void KMPSearch(char* pat, char* txt)
{
    int M = strlen(pat);
    int N = strlen(txt);
  
    // create lps[] that will hold the longest prefix suffix
    // values for pattern
    int lps[M];
  
    // Preprocess the pattern (calculate lps[] array)
    computeLPSArray(pat, M, lps);
  
    int i = 0; // index for txt[]
    int j = 0; // index for pat[]
    while (i < N) {
        if (pat[j] == txt[i]) {
            j++;
            i++;
        }
  
        if (j == M) {
            printf("Found pattern at index %d ", 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;
        }
    }
}
  
// Fills lps[] for given patttern pat[0..M-1]
void computeLPSArray(char* pat, int M, int* lps)
{
    // length of the previous longest prefix suffix
    int len = 0;
  
    lps[0] = 0; // lps[0] is always 0
  
    // the loop calculates lps[i] for i = 1 to M-1
    int i = 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] = 0;
                i++;
            }
        }
    }
}
  
// Driver program to test above function
int main()
{
    char txt[] = "ABABDABACDABABCABAB";
    char pat[] = "ABABCABAB";
    KMPSearch(pat, txt);
    return 0;
}

输出：

Found pattern at index 10

请参阅有关模式搜索的KMP算法的完整文章，以了解更多详细信息！

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