Implement strStr()

Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

The signature of the function had been updated to return the index instead of the pointer.

就是实现字符串匹配，返回匹配的index。有各种算法优化的字符串匹配算法，如：KMP等

但题目只要简单实现就可以，没有时间复杂度的要求。

直接比较子字符串是否等于目标字符串即可。

public static int strStr(String haystack, String needle) {
	int i=0,j=0;
	while(i<=haystack.length()-needle.length()){
		if(!haystack.substring(i,i+needle.length()).equals(needle))
			i++;
		else
			return i;
	}
	return -1;
}