问让我们重温罗马数字

EN

 1  => I
10  => X
 7  => VII

import java.util.HashMap;
import java.util.Map;
import java.util.NavigableMap;
import java.util.TreeMap;

public class RomanNumeral {
  private final int number;
  private static final Map<Integer, String> CACHE = new HashMap<>();

  private static final NavigableMap<Integer, String> NUMBER_TO_ROMAN =
      initMap();

  public RomanNumeral(int number) {
    if (number < 0 || number > 3000) {
      throw new IllegalArgumentException("Number out of range.");
    }
    this.number = number;
  }

  public String getRomanNumeral() {
    if (number == 0) {
      return "";
    }
    String result = CACHE.get(number);
    if (result != null) {
      return result;
    }
    result = toRomen(number);
    CACHE.put(number, result);
    return result;
    //return number == 0 ? "" : toRomen(number);
  }

  private static String toRomen(int num) {
    int floorNum = NUMBER_TO_ROMAN.floorKey(num);
    // Base case
    if (floorNum == num) {
      return NUMBER_TO_ROMAN.get(num);
    }
    return NUMBER_TO_ROMAN.get(floorNum) + toRomen(num - floorNum);
  }

  private static NavigableMap<Integer, String> initMap() {
    NavigableMap<Integer, String> map = new TreeMap<>();
    map.put(1, "I");
    map.put(4, "IV");
    map.put(5, "V");
    map.put(9, "IX");
    map.put(10, "X");
    map.put(40, "XL");
    map.put(50, "L");
    map.put(90, "XC");
    map.put(100, "C");
    map.put(400, "CD");
    map.put(500, "D");
    map.put(900, "CM");
    map.put(1000, "M");
    return map;
  }
}

import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.Parameterized;
import org.junit.runners.Parameterized.Parameters;

import java.util.Arrays;
import java.util.Collection;

import static org.junit.Assert.assertEquals;

@RunWith(Parameterized.class)
public class RomanNumeralsTest {

    private int input;
    private String expectedOutput;

    @Parameters
    public static Collection<Object[]> data() {
        return Arrays.asList(new Object[][]{
                {0, ""},
                {1, "I"},
                {2, "II"},
                {3, "III"},
                {4, "IV"},
                {5, "V"},
                {6, "VI"},
                {9, "IX"},
                {27, "XXVII"},
                {48, "XLVIII"},
                {59, "LIX"},
                {93, "XCIII"},
                {141, "CXLI"},
                {163, "CLXIII"},
                {402, "CDII"},
                {575, "DLXXV"},
                {911, "CMXI"},
                {1024, "MXXIV"},
                {3000, "MMM"}
        });
    }

    public RomanNumeralsTest(int input, String expectedOutput) {
        this.input = input;
        this.expectedOutput = expectedOutput;
    }

    @Test
    public void convertArabicNumberalToRomanNumeral() {
        RomanNumeral romanNumeral = new RomanNumeral(input);

        assertEquals(expectedOutput, romanNumeral.getRomanNumeral());
    }
}