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第12题 数字转为罗马数字
罗马数字采用七个罗马字母作数字、即Ⅰ（1）、X（10）、C（100）、M（1000）、V（5）、L（50）、D（500）。
一开始我按照10进制的思想来做，针对不同区间，编辑不同的罗马表达方式，比如1~9,10~90,100~900,1000~3000
以下是代码：
public static String intToRoman(int num) { // String roman = ""; if(num<=0) return ""; if(num<=10){ String[] tens = new String[]{"I","II","III","IV","V","VI","VII","VIII","IX","X"}; roman = roman+tens[num-1]; } if(10<num && num<100){ //90以内都可以用I V X L表示 String[] ten2nines = new String[] {"X","XX","XXX","XL","L","LX","LXX","LXXX","XC"}; //10,20,30,40,50,60,70,80 int H = ((int) (num/10)); int L = num-H*10; roman = roman + ten2nines[H-1] + intToRoman(L); } if(100<=num && num<1000){ String[] len = new String[] {"C","CC","CCC","CD","D","DC","DCC","DCCC","CM"};//100,200,300,400,500,600,700,800,900 int H = ((int) (num/100)); int L = num-H*100; roman = roman + len[H-1] + intToRoman(L); } if(1000<=num && num <4000){ String[] len = new String[] {"M","MM","MMM"}; int H = ((int) (num/1000)); int L = num-H*1000; System.out.println("H:"+H+",L:"+L); roman = roman + len[H-1] + intToRoman(L); } return roman; }
后来看到网上有一个简便的，先找到所有罗马数字的基，对于十进制，基为（1,2,3,4,5,6,7,8,9,10），罗马数字的基为（"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"），对应数字（1000,900,500,400,100,90,50,40,10,9,5,4,1）
以下为代码：
public static String intToRoman(int num) { String data[] = {"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"}; int value[] = {1000,900,500,400,100,90,50,40,10,9,5,4,1}, base = -1; StringBuilder result = new StringBuilder(); for(int i = 0;i < data.length;i++){ if((base=num/value[i])!=0){ while(base--!=0) result.append(data[i]); num=num%value[i]; } } return result.toString();}
第12题 数字转为罗马数字
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