【leetcode】12. Integer to Roman

题目描述：

Given an integer, convert it to a roman numeral.

Input is guaranteed to be within the range from 1 to 3999.

解题思路：

注意到用例比较少，所以采用以空间换时间的方法，把所有的结果列出，然后组合出输入值n的字符串即可。

具体代码：

 public class Solution {
     public static String intToRoman(int num) {
         String[][] array={
                 {"","I","II","III","IV","V","VI","VII","VIII","IX"},//0-9
                 {"","X","XX","XXX","XL","L","LX","LXX","LXXX","XC"},//10-90
                 {"","C","CC","CCC","CD","D","DC","DCC","DCCC","CM"},//100-900
                 {"","M","MM","MMM"}//1000-3000
         };
         StringBuilder sb = new StringBuilder();
         int n=num/1000;
         sb.append(array[3][n]);
         num=num%1000;

         n=num/100;
         sb.append(array[2][n]);
         num=num%100;

         n=num/10;
         sb.append(array[1][n]);
         num=num%10;

         sb.append(array[0][num]);

         return sb.toString();
     }
 }