12. Integer to Roman

Roman numerals are represented by seven different symbols:  I ,  V ,  X ,  L ,  C ,  D  and  M .

Symbol       Value
I             1
V             5
X             10
L             50
C             100
D             500
M             1000

For example, two is written as II in Roman numeral, just two one's added together. Twelve is written as, XII, which is simply X + II. The number twenty seven is written as XXVII, which is XX + V + II.

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII. Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:

• I can be placed before V (5) and X (10) to make 4 and 9. 
• X can be placed before L (50) and C (100) to make 40 and 90. 
• C can be placed before D (500) and M (1000) to make 400 and 900.

Given an integer, convert it to a roman numeral. Input is guaranteed to be within the range from 1 to 3999.

Example 1:

Input: 3
Output: "III"

Example 2:

Input: 4
Output: "IV"

Example 3:

Input: 9
Output: "IX"

Example 4:

Input: 58
Output: "LVIII"
Explanation: C = 100, L = 50, XXX = 30 and III = 3.

Example 5:

Input: 1994
Output: "MCMXCIV"
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.

翻译

罗马数字包含以下七种字符： I， V， X， L，C，D 和 M。

字符          数值
I             1
V             5
X             10
L             50
C             100
D             500
M             1000

• I 可以放在 V (5) 和 X (10) 的左边，来表示 4 和 9。
• X 可以放在 L (50) 和 C (100) 的左边，来表示 40 和 90。 
• C 可以放在 D (500) 和 M (1000) 的左边，来表示 400 和 900。

在左边表示减掉这个数，在右边表示相加，左边只能有一个，更加详尽的罗马数字规则，如若上题没有明白，请自行百度。

方法呢其实很简单，直接贴代码吧，出自LeetCode社区讨论。思路也很简单，不过虽然很简单，但是老感觉这样写就有点失去了灵魂，不过确实是很简单的写法，否则就得写一堆swith case

public static String intToRoman(int num) {
    String M[] = {"", "M", "MM", "MMM"};
    String C[] = {"", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"};
    String X[] = {"", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"};
    String I[] = {"", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"};
    return M[num/1000] + C[(num%1000)/100] + X[(num%100)/10] + I[num%10];
}

点击查看更多解法

既然直接复制了LeetCode社区中的代码，那么自己再另外写一份好了。

转换罗马数字，在国内用的还是挺少的，特别是这种大额的，但是将数字转换汉字在一些行业应用就比较多了。那么我们就试着将数字转换为汉字试试吧。

下面直接上代码，思路就不多说了，和上面类似，挺简单的。

    public String intToHanzi(long num) {
        String[] symbols = {"", "拾", "佰", "仟", "万", "亿"};
        String[] values = {"零", "壹", "贰", "叁", "肆", "伍", "陆", "柒", "捌", "玖"};
        String unit = "圆";
        long digit = 10;
        int i = 0;
        StringBuilder sb = new StringBuilder();
        long temp = num;
        do {
            int number = (int) (num % digit / (digit / 10));
            digit *= 10;
            temp /= 10;
            sb.append(getUnit(symbols, number, i));
            sb.append(values[number]);
            i++;
        }while (temp != 0);
        return sb.reverse().append(unit).toString();
    }

    private String getUnit(String[] symbols, int value, int i){
        if (value == 0) return "";
        if (i - 8 > 0){
            return symbols[i - 8];
        }else if (i - 8 == 0){
            return symbols[5];
        }else if (i - 4 > 0){
            return symbols[i - 4];
        }else {
            return symbols[i];
        }
    }

测试了一下，输入"245812039L"进行转换之后"贰亿肆仟伍佰捌拾壹万贰仟零叁拾玖圆"是不是以后读数字再也不用先数位数，然后再读出来了。

如果各位看官有更好的思路欢迎交流。