GeeksforGeeks（C語言KMP）

原網址：https://www.geeksforgeeks.org/kmp-algorithm-for-pattern-searching/

（1）求lps數組，分兩種情況判斷，匹配前一段字符串最大相等前綴和後綴分別添加一個字符的情況

（2）相等情況，動態規劃，不等情況，回溯法：利用傳遞性，a=b,b=c,那麼a=c

（3）匹配字符串，注意利用前綴和後綴的最大相等長度

// C++ program for implementation of KMP pattern searching 
// algorithm 
#include <bits/stdc++.h> 

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]) { //相等，動態規劃
	    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]; //不等，利用傳遞性，a=b,b=c,那麼a=c

	    // 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; 
} 

這篇博客寫的不錯，這兩篇結合起來看了好久纔看懂KMP，這種東西一般都是意會，頑張って

https://blog.csdn.net/qq_37174526/article/details/90141833