Implement strStr()

Implement strStr().

Returns a pointer to the first occurrence of needle in haystack, or null if needle is not part of haystack.

思想：一个一个匹配，注意终止条件；要相对严格限制

1. char *strStr(char *haystack, char *needle) {
2. int i=0;
3. int hlen = strlen(haystack);
4. int nlen = strlen(needle);
5. while(i<=hlen-nlen) {
6. char *p = haystack;
7. char *q = needle;
8. while(*p!='\0' && *p == *q) {
9. p++;
10. q++;
11. }
12. if(*q=='\0') {
13. return p-(q-needle);
14. } else {
15. haystack++;
16. i++;
17. }
18. }
19. return NULL;
20. }