C++

(1) null

(2) length is 0

(3) return value

(4) strlen

1 class Solution { 2 public: 3     /** 4      * Returns a index to the first occurrence of target in source, 5      * or -1  if target is not part of source. 6      * @param source string to be scanned. 7      * @param target string containing the sequence of characters to match. 8      */ 9     int strStr(const char *source, const char *target) {10         // write your code here11         if (source == NULL || target == NULL) return -1;12         13         int i, j, len_s = strlen(source), len_t = strlen(target);14         15         if (len_s == 0 && len_t == 0) return 0;16         17         i = 0;18         while (source[i] != '\0') {19             if (i + len_t > len_s) return -1;20             j = 0;21             while (target[j] != '\0') {22                 if (source[i + j] == target[j]) {23                     j++;24                 } else {25                     break;26                 }27             }28             if (target[j] == '\0')  return i;29             i++;30         }31         return -1;32     }33 };