public int strStr(String haystack, String needle) {
        if (needle.length() > haystack.length()){
            return -1;
        }
        if (needle.equals("")){
            return 0;
        }
        Map<Character,Integer> map = new HashMap<Character, Integer>();
        for (int i=0; i<needle.length(); i++){
            map.put(needle.charAt(i), i);
        }
        int result = -1;
        boolean match = false;
        int i=0;
        while (i<haystack.length()){
            int itemp = i;
            int j=0;
            while (j<needle.length()){
                //处理itemp越界
                if (itemp>=haystack.length()) return -1;
                if (haystack.charAt(itemp) != needle.charAt(j)){
                    //处理跳跃的时候越界
                    if (i+needle.length() >= haystack.length()){
                        return -1;
                    }
                    char next = haystack.charAt(i + needle.length());
                    //遍历查找next是否在needle中出现
                    Integer nextpos = map.get(next);
                    if (nextpos == null){
                        i += needle.length();
                    }else{
                        //有匹配，则最后匹配的地方对齐
                        i += needle.length() - nextpos - 1;
                    }
                    break;
                }
                //成功匹配
                if (j == needle.length()-1){
                    match = true;
                    result = i;
                    break;
                }
                j++;
                itemp++;
            }
            if (match == true){
                break;
            }
            i++;
        }

        return result;
    }