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 
# include <string.h>
# include 

/* 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        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 
# 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;
}

转载于:https://www.cnblogs.com/JMDWQ/archive/2012/02/20/2360539.html