实现strStr()函数

方法一：暴力解法

 int strStr(string haystack, string needle) {
     if (needle.empty())
         return ;

     int M = haystack.size();
     int N = needle.size();

     for (int i = ; i <= M - N; i++)
     {
         int j;
         for (j = ; j < N; j++)
         {
             if (needle[j] != haystack[i + j])
             {
                 break;
             }
         }
         if (j == N)
             return i;
     }
     return -;
 }

方法二：利用memcmp，一层for循环即可解决

 int strStr(string haystack, string needle) {
     if (needle.empty())
         return ;

     int M = haystack.size();
     int N = needle.size();

     char* m = new char[M + ];
     char* n = new char[N + ];

     memcpy(m, haystack.c_str(), M);
     memcpy(n, needle.c_str(),    N);
     m[M] = '\0';
     n[N] = '\0';

     for (int i = ; i <= M - N; i++)
     {
         if ( == memcmp(&m[i], n, N))
         {
             delete[] m;
             delete[] n;
             return i;
         }
     }

     delete[] m;
     delete[] n;

     return -;
 }

方法三： KMP算法