leetcode 之Implement strStr()（27）

char *strStr(char *haystack, char*needle)
      {
          char* p1;
          char* p2;
          char* p1_advance=haystack;

          //当字符串数量不足时，直接停止匹配
          for (p2 = &needle[1]; *p2; p2++)
              p1_advance++;

          for (p1 = haystack; *p1_advance; p1_advance++)
          {
              char *p1_old = p1;
              p2 = needle;
              while (*p1 && *p2 && *p1 == *p2)
              {
                  p1++;
                  p2++;
              }
              if (!*p2)return p1_old;

              p1 = p1_old + 1;
          }

          return nullptr;
      }