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;
    }
};