字符串匹配KMP算法

详细算法描述见《算法导论32.4》，以下是C实现：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

//预处理：所需时间为O(m)，空间O(m)
void compute_prefix_func(char sp[], int p[])
{
    int m, k, q;
    m = strlen(sp);
    p[0] = 0;
    k = 0;
    for (q = 1; q < m; q++) {
        while ((k > 0) && (sp[k] != sp[q])) {
            k = p[k-1];
        }
        if (sp[k] == sp[q])
            k++;
        p[q] = k;
    }
    
    for (q = 0; q < m; q++)
        printf("p[%d] = %d\n", q, p[q]);
}

//匹配：所需时间为O(n)
void kmp_matcher(char st[], char sp[])
{
    int n, m, q, i;
    int *p;
    n = strlen(st);
    m = strlen(sp);
    p = (int *)malloc(sizeof(int) * m);
    compute_prefix_func(sp, p);
    q = 0; //Number of characters matched
    for (i = 0; i < n; i++) {
        while ((q > 0) && (sp[q] != st[i])) {
            q = p[q-1]; //Next character does not match
        }
        if (sp[q] == st[i]) //Next character matches
            q++;
        if (q == m) { //Is all of P matched?
            printf("Pattern occurs with shift %d\n", i - (m - 1));
            q = p[q-1]; //Look for the next match
        }
    }
    free(p);
}

int main(void)
{
    char st[] = "abcdabcabcabcabcdabcabcdabcabcabcd";
    char sp[] = "abcabcd";
    kmp_matcher(st, sp);
    return 1;
}

KMP算法图文解析

KMP算法详解