Roman Numeral Reduction

ardallie · ardallie · commit fe1c8e2439ef · 2021-08-18T00:34:19.000+01:00
diff --git a/src/hard/RomanNumReduction.java b/src/hard/RomanNumReduction.java
@@ -0,0 +1,91 @@
+package hard;
+
+import java.util.HashMap;
+
+/**
+ * Have the function RomanNumeralReduction(str) read str
+ * which will be a string of roman numerals in decreasing order.
+ * The numerals being used are: I for 1, V for 5, X for 10,
+ * L for 50, C for 100, D for 500 and M for 1000.
+ * Your program should return the same number given
+ * by str using a smaller set of roman numerals.
+ * For example: if str is "LLLXXXVVVV" this is 200, so your program should return CC
+ * because this is the shortest way to write 200 using the roman numeral system given above.
+ * If a string is given in its shortest form, just return that same string.
+ */
+public class RomanNumReduction {
+
+  private static final HashMap<String, Integer> romans = new HashMap<>() {
+    {
+      put("M", 1000);
+      put("D", 500);
+      put("C", 100);
+      put("L", 50);
+      put("X", 10);
+      put("V", 5);
+      put("I", 1);
+    }
+  };
+
+  private static final String[] orderedRomans = new String[]{"M", "D", "C", "L", "X", "V", "I"};
+
+  /**
+   * Calculate the sum for an expression.
+   *
+   * @param exp expression
+   * @return a sum
+   */
+  public static int sumRomans(String exp) {
+    int result = 0;
+    String[] tokens = exp.toUpperCase().split("");
+    for (String token : tokens) {
+      result += romans.get(token);
+    }
+    return result;
+  }
+
+  /**
+   * Reduce Roman numerals.
+   *
+   * @param sum a number
+   * @return a string of Roman numerals
+   */
+  public static String reduceRomans(int sum) {
+    StringBuilder output = new StringBuilder();
+    int remainder = sum;
+    for (String numeral : orderedRomans) {
+      Integer val = romans.get(numeral);
+      while (remainder / val >= 0 && remainder - val >= 0) {
+        output.append(numeral);
+        remainder -= val;
+      }
+    }
+    return output.toString();
+  }
+
+  /**
+   * Roman Numeral Reduction function.
+   *
+   * @param str input string
+   * @return result
+   */
+  public static String romanNumeralReduction(String str) {
+    int sum = sumRomans(str);
+    return reduceRomans(sum);
+  }
+
+  /**
+   * Entry point.
+   *
+   * @param args command line arguments
+   */
+  public static void main(String[] args) {
+    String result1 = romanNumeralReduction("XXXVVIIIIIIIIII");
+    System.out.println(result1);
+    String result2 = romanNumeralReduction("VVV");
+    System.out.println(result2);
+    String result3 = romanNumeralReduction("CCCCCIIIII");
+    System.out.println(result3);
+  }
+
+}
