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Task/Roman-numerals-Encode/Java/roman-numerals-encode-2.java

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+import java.util.Set;
+import java.util.EnumSet;
+import java.util.Collections;
+import java.util.stream.Collectors;
+import java.util.stream.LongStream;
+
+public interface RomanNumerals {
+  public enum Numeral {
+    M(1000), CM(900), D(500), CD(400), C(100), XC(90), L(50), XL(40), X(10), IX(9), V(5), IV(4), I(1);
+
+    public final long weight;
+
+    private static final Set<Numeral> SET = Collections.unmodifiableSet(EnumSet.allOf(Numeral.class));
+
+    private Numeral(long weight) {
+      this.weight = weight;
+    }
+
+    public static Numeral getLargest(long weight) {
+      return SET.stream()
+        .filter(numeral -> weight >= numeral.weight)
+        .findFirst()
+        .orElse(I)
+      ;
+    }
+  };
+
+  public static String encode(long n) {
+    return LongStream.iterate(n, l -> l - Numeral.getLargest(l).weight)
+      .limit(Numeral.values().length)
+      .filter(l -> l > 0)
+      .mapToObj(Numeral::getLargest)
+      .map(String::valueOf)
+      .collect(Collectors.joining())
+    ;
+  }
+
+  public static long decode(String roman) {
+    long result =  new StringBuilder(roman.toUpperCase()).reverse().chars()
+      .mapToObj(c -> Character.toString((char) c))
+      .map(numeral -> Enum.valueOf(Numeral.class, numeral))
+      .mapToLong(numeral -> numeral.weight)
+      .reduce(0, (a, b) -> a + (a <= b ? b : -b))
+    ;
+    if (roman.charAt(0) == roman.charAt(1)) {
+      result += 2 * Enum.valueOf(Numeral.class, roman.substring(0, 1)).weight;
+    }
+    return result;
+  }
+
+  public static void test(long n) {
+    System.out.println(n + " = " + encode(n));
+    System.out.println(encode(n) + " = " + decode(encode(n)));
+  }
+
+  public static void main(String[] args) {
+    LongStream.of(1999, 25, 944).forEach(RomanNumerals::test);
+  }
+}