短网址算法 - 爱码网

    //62进制
    public static int BASE_NUM = 62;

    //62进制字母顺序
    public static final char[] array = {\'G\', \'q\', \'w\', \'0\', \'H\', \'e\', \'T\', \'F\', \'9\', \'r\', \'V\', \'t\', \'y\', \'u\', \'N\', \'i\', \'6\', \'D\', \'o\', \'p\', \'L\', \'a\', \'s\', \'d\', \'K\', \'f\', \'g\', \'h\', \'j\', \'k\', \'4\', \'l\', \'z\', \'x\', \'c\', \'v\', \'b\', \'S\', \'n\', \'m\', \'1\', \'Z\', \'3\', \'5\', \'Q\', \'W\', \'E\', \'R\', \'7\', \'Y\', \'U\', \'I\', \'O\', \'2\', \'P\', \'A\', \'J\', \'X\', \'C\', \'B\', \'8\', \'M\'};

    /**
     * 将10进制数转为62进制字符串(短网址)
     *
     * @param number
     * @return
     */
    public static String getShortUrlByLongNum(Long number) {
        Long rest = number;
        Stack<Character> stack = new Stack<Character>();
        StringBuilder result = new StringBuilder(0);
        if (0 == rest) {
            return String.valueOf(array[0]);
        }
        while (rest != 0) {
            stack.add(array[new Long((rest - (rest / BASE_NUM) * BASE_NUM)).intValue()]);
            rest = rest / BASE_NUM;
        }
        for (; !stack.isEmpty(); ) {
            result.append(stack.pop());
        }
        return result.toString();
    }

    /**
     * 通过短网址返回10进制数
     *
     * @param shortUrl
     * @return
     */
    public static Long getLongNumByShortUrl(String shortUrl) {
        long multiple = 1;
        long result = 0;
        Character c;
        for (int i = 0; i < shortUrl.length(); i++) {
            c = shortUrl.charAt(shortUrl.length() - i - 1);
            result += valueOfCharacter(c) * multiple;
            multiple = multiple * BASE_NUM;
        }
        return result;
    }

    /**
     * 字母对应的值 如array数组 G对应0 q对应1
     *
     * @param c
     * @return
     */
    private static int valueOfCharacter(Character c) {
        for (int i = 0; i < array.length; i++) {
            if (c == array[i]) {
                return i;
            }
        }
        return -1;
    }

准备一个被打乱的数组，存放A-Za-Z0-9这62个字符，预先产生一个网址ID，将这个ID通过 _10_to_62 解析转换成62进制的短网址符。

存储ID,短网址code，页面URL 算法如下，很简单，时间效率也比较高，甚至，有了存储的ID，要不要存储短网址code都无所谓，

这个算法时间复杂度本来就是n，而一般的短网址长度也就1~7位，时间复杂度也可以算作O(1)常量了。