My attempt from video.

src/main/java/org/ea/Roman.java

@@ -1,7 +1,59 @@
 package org.ea;
 
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
 public class Roman {
+    static Map<Integer, String> roman = new HashMap<>();
+    static List<Integer> romanNum = new ArrayList<>();
+
+    static {
+        roman.put(1000, "M");
+        roman.put(900, "CM");
+        roman.put(500, "D");
+        roman.put(400, "CD");
+        roman.put(100, "C");
+        roman.put(90, "XC");
+        roman.put(50, "L");
+        roman.put(40, "XL");
+        roman.put(10, "X");
+        roman.put(9, "IX");
+        roman.put(5, "V");
+        roman.put(4, "IV");
+        roman.put(1, "I");
+
+        romanNum.add(1000);
+        romanNum.add(900);
+        romanNum.add(500);
+        romanNum.add(400);
+        romanNum.add(100);
+        romanNum.add(90);
+        romanNum.add(50);
+        romanNum.add(40);
+        romanNum.add(10);
+        romanNum.add(9);
+        romanNum.add(5);
+        romanNum.add(4);
+        romanNum.add(1);
+    }
+
+
     public static String numToRoman(int number) {
-        return null;
+        if (number < 0) {
+            return null;
+        }
+        if (number > 3999) {
+            return null;
+        }
+
+        for (Integer num : romanNum) {
+            if (number > 0 && ((double)number / (double)num) >= 1d) {
+                number -= num;
+                return roman.get(num) + numToRoman(number);
+            }
+        }
+        return "";
     }
 }