【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();
    }
}