Integer to Roman

Given an integer, convert it to a roman numeral.

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

没啥算法技术含量，搞明白Roman Integer的构造，按照千位，百位，十位和个位的数字来加一加就行了。

public class Solution {
    public String intToRoman(int num) {
        StringBuilder builder = new StringBuilder();
        int thousand = num / 1000;
        for(int i = 1; i <= thousand; i++){
            builder.append("M");
        }
        
        int hundred = num % 1000 / 100;
        //900
        if(hundred == 9)
            builder.append("CM");
        //0~400
        else if(hundred < 4){
            for(int i = 1; i <= hundred; i++)
                builder.append("C");
        }
        //400
        else if(hundred == 4){
            builder.append("CD");
        }
        //500~800
        else{
            builder.append("D");
            for(int i = 6; i <= hundred; i++)
                builder.append("C");
        }
        
        int tens = num % 100 / 10;
        //90
        if(tens == 9)
            builder.append("XC");
        //0~40
        else if(tens < 4){
            for(int i = 1; i <= tens; i++)
                builder.append("X");
        }
        //40
        else if(tens == 4){
            builder.append("XL");
        }
        //50~80
        else{
            builder.append("L");
            for(int i = 6; i <= tens; i++)
                builder.append("X");
        }
        
        int ones = num % 10;
         //9
        if(ones == 9)
            builder.append("IX");
        //0~4
        else if(ones < 4){
            for(int i = 1; i <= ones; i++)
                builder.append("I");
        }
        //4
        else if(ones == 4){
            builder.append("IV");
        }
        //5~8
        else{
            builder.append("V");
            for(int i = 6; i <= ones; i++)
                builder.append("I");
        }
        return builder.toString();
    }
}