Implement strStr().
Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
Update (2014-11-02):
The signature of the function had been updated to return the index instead of the pointer. If you still see your function signature returns a char * or String, please click the reload button to reset your code definition.
解题：我用的方法相当于暴力破解：int strStr(string haystack, string needle) ；
首先，遍历haystack，依次寻找第一个与needle第一个字符匹配的位置，同时记录相对于该位置的下一个位置（我记为ret，一旦接下来的匹配不成功，重新遍历haystack时，就从ret开始），如果遍历完haystack都没匹配成功，则返回-1。注意边界条件！！
我的源代码如下：
1 class Solution { 2 public: 3 int strStr(string haystack, string needle) { 4 if(needle.empty()) 5 return 0; 6 if (haystack.empty()) 7 { 8 if(!needle.empty()) 9 return -1; 10 } 11 if(needle.size()>haystack.size()) 12 return -1; 13 int index = 0, reset = -1; 14 while (index < haystack.size()) 15 { 16 if (haystack[index] != needle[0]) 17 { 18 index++; 19 continue; 20 } 21 reset = index + 1; 22 int i; 23 for ( i = 1;index+needle.size()<=haystack.size()&& i < needle.size(); ++i) 24 { 25 if (haystack[index + i] != needle[i]) 26 break; 27 } 28 if (i == needle.size()) 29 return index ; 30 else index = reset; 31 } 32 return -1; 33 } 34 };