[Leetcode] implement strStr() (C++)

Github leetcode 我的解题仓库   https://github.com/interviewcoder/leetcode

题目：

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.

Tag:

String; Two Pointers

体会：

这道题是字符串的匹配问题，目前还只会朴素的逐步方法，但是这道题还有KMP解法，和Boyer-Moore的解法，目前还没有掌握。

先把笔记放到这里，以后再来解决吧。

1. KMP算法

2. Boyer-Moore算法

class Solution {
public:
    int strStr(char *haystack, char *needle) {
        int i = 0;  // index under examine in haystack
        int j = 0;  // index under examine in needle
        
        while (haystack[i] && needle[j]) {
            if (haystack[i] == needle[j]) {
                i++;
                j++;
            } else {
                // roll back:
                // reset haystack index back to (i - j + 1), since in current examine
                // start index in haystack is (i - j)
                i = i - j + 1;
                // reset needle back to its beginning
                j = 0;
            }
        }
        // if haystack ends but needle not ends, 
        // we know needle is not in the haystack, then return -1.
        return (needle[j]) ? -1 : (i - j);
    }
};