1 class Solution { 2 public: 3 int strStr(char *haystack, char *needle) { 4      5     int i = 0 , skip[256]; 6     char *str = haystack, *substr = needle; 7     int len_src = strlen(str), len_sub = strlen(substr); 8     // preprocess 9     for (i = 0; i < 256; i++)10         skip[i] = len_sub;11     int last = len_sub - 1;12     for (i = 0; i < last;i++)13         skip[substr[i]] = last - i;14     // search15     int pos = 0,  j;16     while (pos <= len_src-len_sub)  {17         j = last;18         while (j>=0 && str[pos+j]==substr[j])19             j--;20         if (j<0) 21              return pos;22         pos += skip[str[pos+last]];23     }24     return -1;25 }26 };