KMP算法实现

/* * ===================================================================================== * * Filename: kmp.cpp * * Description: KMP算法实现 * * Version: 1.0 * Created: 2009年02月13日 13时19分20秒 * Revision: none * Compiler: g++ * * Author: Shiquan Ye (mn), yeshiquan@gmail.com * Company: Wuhan University * * ===================================================================================== */ #include <iostream> #include <string.h> using namespace std; int *compute_prefix_function (char *p) { int m = strlen(p); int k = 0; int *x = new int[m]; x[0] = 0; for (int q = 2; q <= m; q++) { while (k > 0 && p[k] != p[q-1]) k = x[k-1]; if (p[k] == p[q-1]) k++; x[q-1] = k; } return x; } void kmp_matcher(char *t, char *p) { int n = strlen(t); int m = strlen(p); int *x = compute_prefix_function(p); int q = 0; /* Number of characters mached */ for (int i = 0; i < n; i++) { /* Scan the text from left to right */ while (q > 0 && p[q] != t[i]) q = x[q-1]; /* Next character does not match */ if (p[q] == t[i]) q++; /* Next character matches */ if (q == m) { /* Is all of p matched */ cout<<"Pattern occurs with shift "<<i-m+1<<endl; q = x[q-1]; /* Look for the next match */ } } } int main() { char *t = "123abcdefg123hijk123"; char *p = "123"; kmp_matcher(t, p); return 0; }

运行结果：

Pattern occurs with shift 0
Pattern occurs with shift 10
Pattern occurs with shift 17

 

说明：

算法原理参见算法导论第32章

《算法导论》的字符串第一个位置从1开始，为了不浪费空间，这个程序的字符串的第一个位置从0开始，所以：

Pq表示字符串P[0...q-1]

x[q]表示字符串Pq+1的最长后缀的长度