字符串循环移位查找子字符串

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

int findSubString(const char *s, int slen, const char *d);
int parseString(char *s, int slen, const char *d);

int
main(void)
{
        char s[] = "ABBCD";
        char d[] = "DA";
        int len = strlen(s);

        printf("s = %s, d = %s\n", s, d);
        printf("Res = %d\n", findSubString(s, len, d));
        printf("s = %s, d = %s\n", s, d);
        printf("Res = %d\n", parseString(s, len, d));
        printf("s = %s, d = %s\n", s, d);

        return (0);
}

//双循环，费时间
int
parseString(char *s, int len, const char *d)
{
        int i = 0;
        int j = 0;

        if (strstr(s, d)) {
                return (0);
        }

        for (i = 0; i < len; i++) {
                char ctmp = *s;
                for (j = 1; j < len; j++) {
                        *(s+j-1) = *(s+j);
                }
                *(s+j-1) = ctmp;

                if (strstr(s, d)) {
                        return (0);
                } else {
                        return (-1);
                }
        }

        return (-1);
}

//先分析后处理，空间换时间
int
findSubString(const char *s, int slen, const char *d)
{
        char ss[slen*2];

        strcpy(ss,s);
        strcpy(ss+slen, s);

        if (strstr(ss,d)) {
                return (0);
        } else {
                return (-1);
        }
}