KMPmatch 字符串模式匹配

O(m+n)

计算后缀数组时，子串进行的也是模式匹配。

/* KMP match */
# include <stdio.h>
# include <string.h>
# include <stdlib.h>

/* P in T */
int KMPmatch(char *T, char *P)
{
    int n, m;
    int i, j, k, *next;

    n = strlen(T);
    m = strlen(P);

    next = (int *)malloc((m-1)*sizeof(int));

    /* compute postfix : next[] */
    next[0] = -1;
    k = -1;
    for (i = 1; i < m; ++i)
    {
        while (k>=0 && P[k+1]!=P[i])
            k = next[k];
        if (P[k+1] == P[i]) ++k;
        next[i] = k;
    }

    /*
    for (i=0; i<m; ++i)
        printf("%d ", next[i]+1);
    putchar('\n');
    */

    /* pattern match */
    i = -1;
    for (j = 0; j < n; ++j)
    {
        while (i>=0 && P[i+1]!=T[j])
            i = next[i];
        if (P[i+1] == T[j]) ++i;
        if (i == m-1) return (j-m+1);
        /*
        if (i == m-1)
        {
            printf("Pattern occurs with shift: %d\n", j-m+1);
            i = next[i];
        }
         */
    }

    return -1;
}

int main()
{
    int i;

    i = KMPmatch("Heababababcaf", "ababababca");
    printf("index in T: %d\n", i);

    return 0;
}

strstr的用法：

/* strstr */
# include <stdio.h>
# include <string.h>
int main()
{
    char T[] = "Hello, world";
    char P[] = "ello, ";
    char *ptr;

    ptr = strstr(T, P);
    if (ptr != NULL) printf("%d %c\n", ptr-T, *ptr);
    else printf("dismatch\n");

    return 0;
}