1 int *find_next(char *p)

 2 {

 3     int k = -1;                            //right shift i-k

 4     int i = 0;

 5     int m = strlen(p);

 6     int *next = (int *)malloc(sizeof (int) * m);

 7     next[0] = -1;

 8                                         //maintain the k is the length of longest matching prefix of p[i]

 9     while (i < m-1) {                    //after i++, i == m-1, the last index of element in next[]

10         while (k >= 0 && p[i] != p[k])    //how to assure the k is the length of longest matching substring of p[i]??

11             k = next[k];

12         i++;

13         k++;

14         next[i] = k;

15     }

16     return next;

17 }