关于罗马数字：
I: 1
V: 5
X: 10
L: 50
C: 100
D: 500
M: 1000
字母可以重复，但不超过三次，当需要超过三次时，用与下一位的组合表示：
I: 1, II: 2, III: 3, IV: 4
C: 100, CC: 200, CCC: 300, CD: 400
提取每一位digit，然后convert to 罗马数字
public class Solution {
private static char[][] chars = {{'I', 'V'}, {'X', 'L'}, {'C', 'D'}, {'M', 'O'}};
public String intToRoman(int num) {
int copy_num = num;
int count = 0;
StringBuilder result = new StringBuilder();
while (copy_num != 0) {
int x = copy_num / 10;
int digit = copy_num - x * 10;
switch (digit) {
case 3: result.append(chars[count][0]);
case 2: result.append(chars[count][0]);
case 1: result.append(chars[count][0]);
case 0: break;
case 4: result.append(chars[count][1]); result.append(chars[count][0]); break;
case 8: result.append(chars[count][0]);
case 7: result.append(chars[count][0]);
case 6: result.append(chars[count][0]);
case 5: result.append(chars[count][1]); break;
case 9: result.append(chars[count + 1][0]); result.append(chars[count][0]); break;
}
count++;
copy_num = x;
}
result = result.reverse();
return result.toString();
}
}