相互转换的过程很简单，但是首先第一步就是要搞清楚罗马数字的规律，还是ting有意思的~~~
罗马数字总共有七种字符，对应的数字如下：
I 1
V 5
X 10
L 50
C 100
D 500
M 1000
如：I,II,III,IV,V,VI,VII,VIII,IX,X分别对应1，2，3，4，5，6，7，8，9,10。可以发现小于4的，就是I一直叠加，4（IV）是右边的数减去左边的数，大于V小于X就是右边的数加上左边的数，以此类推。。。
下面分别是罗马数转整数和整数转罗马数：
import java.util.HashMap;
import java.util.Scanner;
public class RomanAndInt {
//罗马数转整数
public int RomanToInt(){
Scanner sc =new Scanner(System.in);
String Lnumber=sc.next();
if(Lnumber==null|| Lnumber.length()==0){
return -1;
}
HashMap map=new HashMap();
map.put('I',1);
map.put('V',5);
map.put('X',10);
map.put('L',50);
map.put('C',100);
map.put('D',500);
map.put('M',1000);
int result=map.get(Lnumber.charAt(Lnumber.length()-1));
for(int i=Lnumber.length()-2;i>=0;i--){
if(map.get(Lnumber.charAt(i))>=map.get(Lnumber.charAt(i+1))){
result+=map.get(Lnumber.charAt(i));
}else{
result-=map.get(Lnumber.charAt(i));
}
}
return result;
}
//整数转罗马数
public String IntToRoman(){
Scanner sc=new Scanner(System.in);
int number=sc.nextInt();
StringBuilder sb=new StringBuilder();
String[][] roman={
{"","I","II","III","IV","V","VI","VII","VIII","IX"},
{"","X","XX","XXX","XL","L","LX","LXX","LXXX","XC"},
{"","C","CC","CCC","CD","D","DC","DCC","DCCC","CM"},
{"","M","MM","MMM"}
};
sb.append(roman[3][number/1000%10]);
sb.append(roman[2][number/100%10]);
sb.append(roman[1][number/10%10]);
sb.append(roman[0][number%10]);
String result=""+sb;
return result;
}
public static void main(String[] args){
RomanAndInt re=new RomanAndInt();
re.RomanToInt();
re.IntToRoman();
}
}
