Basic Roman Numerals

ardallie · ardallie · commit adc795de93f0 · 2021-08-11T23:11:27.000+01:00
diff --git a/src/easy/BasicRomanNumerals.java b/src/easy/BasicRomanNumerals.java
@@ -0,0 +1,62 @@
+package easy;
+
+import java.util.HashMap;
+
+/**
+ * Have the function BasicRomanNumerals(str) read str which will be a string of Roman numerals.
+ * 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.
+ * In Roman numerals, to create a number like 11 you simply add a 1 after the 10,
+ * so you get XI. But to create a number like 19, you use the subtraction notation
+ * which is to add I before an X or V (or add an X before an L or C).
+ * So 19 in Roman numerals is XIX.
+ * ---
+ * The goal of your program is to return the decimal equivalent of the Roman numeral given.
+ * For example: if str is "XXIV" your program should return 24
+ */
+public class BasicRomanNumerals {
+
+  /**
+   * Basic Roman Numerals function.
+   *
+   * @param str input string
+   * @return the decimal equivalent of the Roman numeral given
+   */
+  private static int basicRomanNumerals(String str) {
+    HashMap<String, Integer> numerals = new HashMap<>();
+    numerals.put("M", 1000);
+    numerals.put("D", 500);
+    numerals.put("C", 100);
+    numerals.put("X", 10);
+    numerals.put("L", 50);
+    numerals.put("V", 5);
+    numerals.put("I", 1);
+    // reversing the string makes the parsing easier
+    char[] reversed = new StringBuilder(str).reverse().toString().toCharArray();
+    int result = 0;
+    int prevValue = 0;
+    for (char cr : reversed) {
+      int thisValue = numerals.get(Character.toString(cr));
+      if (thisValue > prevValue) {
+        result += thisValue;
+      } else {
+        result -= thisValue;
+      }
+      prevValue = thisValue;
+    }
+    return result;
+  }
+
+  /**
+   * Entry point.
+   *
+   * @param args command line arguments
+   */
+  public static void main(String[] args) {
+    var result1 = basicRomanNumerals("XXIV");
+    System.out.println(result1);
+    var result2 = basicRomanNumerals("XLVI");
+    System.out.println(result2);
+  }
+
+}
