Java实现的求解经典罗马数字和阿拉伯数字相互转换问题示例

import java.util.Scanner;
/**
 * 请编写程序，由用户输入若干个罗马数字串，程序输出对应的十进制表示。
 *
 * 输入格式是：第一行是整数n,表示接下来有n个罗马数字(n<100)。以后每行一个罗马数字。罗马数字大小不超过999。
 *
 * 要求程序输出n行，就是罗马数字对应的十进制数据。
 *
 * 例如，用户输入： 3 LXXX XCIII DCCII
 *
 * 则程序应该输出： 80 93 702
 *
 * @author Administrator
 *
 */
public class RomeToArabic {
  public static void main(String[] args) {
    // TODO Auto-generated method stub
    System.out.println("测试结果：");
    Scanner mScanner = new Scanner(System.in);
    System.out.println(r2a(mScanner.nextLine()));
    System.out.println(a2r(mScanner.nextInt()));
  }
  /**
   * 把罗马数字转换为阿拉伯数字
   *
   * @param m
   * @return
   */
  public static int r2a(String m) {
    int graph[] = new int[400];
    graph['I'] = 1;
    graph['V'] = 5;
    graph['X'] = 10;
    graph['L'] = 50;
    graph['C'] = 100;
    graph['D'] = 500;
    graph['M'] = 1000;
    char[] num = m.toCharArray();
    int sum = graph[num[0]];
    for (int i = 0; i < num.length - 1; i++) {
      if (graph[num[i]] >= graph[num[i + 1]]) {
        sum += graph[num[i + 1]];
      } else {
        sum = sum + graph[num[i + 1]] - 2 * graph[num[i]];
      }
    }
    return sum;
  }
  /**
   * 把阿拉伯数字转换为罗马数字
   *
   * @param number
   * @return
   */
  public static String a2r(int number) {
    String rNumber = "";
    int[] aArray = { 1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1 };
    String[] rArray = { "M", "CM", "D", "CD", "C", "XC", "L", "XL", "X",
        "IX", "V", "IV", "I" };
    if (number < 1 || number > 3999) {
      rNumber = "-1";
    } else {
      for (int i = 0; i < aArray.length; i++) {
        while (number >= aArray[i]) {
          rNumber += rArray[i];
          number -= aArray[i];
        }
      }
    }
    return rNumber;
  }
}