Implement strStr().

Returns a pointer to the first occurrence of needle in haystack, or null if needle is not part of haystack.

https://oj.leetcode.com/problems/implement-strstr/

思路：目测有BF法，BMP法，BM法等。

BF法

public class Solution {	public String strStr(String hayStack, String needle) {		if (hayStack == null || needle == null)			return null;		int hayLen = hayStack.length();		int neeLen = needle.length();		if (hayLen < neeLen)			return null;		int i, j;		int hayStart = 0;		while (hayStart <= hayLen-neeLen) {			i = hayStart;			j = 0;			while (i < hayLen && j < neeLen					&& hayStack.charAt(i) == needle.charAt(j)) {				i++;				j++;			}			if (j == neeLen) {				return hayStack.substring(hayStart);			}			hayStart++;		}		return null;	}	public static void main(String[] args) {		System.out.println(new Solution().strStr("abcdefg", "cde"));		System.out.println(new Solution().strStr("cde", ""));		System.out.println(new Solution().strStr("aaabbb", "abbb"));		System.out.println(new Solution().strStr("", ""));			}}

参考：

http://blog.csdn.net/kenden23/article/details/17029625

http://fisherlei.blogspot.com/2012/12/leetcode-implement-strstr.html