Implement strStr() leetcode

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：

class Solution {
public:
int strStr(string haystack, string needle) {
if(needle.empty())
return 0;
if (haystack.empty())
{
if(!needle.empty())
return -1;
}
if(needle.size()>haystack.size())
return -1;
int index = 0, reset = -1;
while (index < haystack.size())
{
if (haystack[index] != needle[0])
{
index++;
continue;
}
reset = index + 1;
int i;
for ( i = 1;index+needle.size()<=haystack.size()&& i < needle.size(); ++i)
{
if (haystack[index + i] != needle[i])
break;
}
if (i == needle.size())
return index ;
else index = reset;
}
return -1;
}
};