Add a server for solving the hanoi puzzle

app/src/main/java/ch/nuth/zhaw/exbox/HanoiServer.java

@@ -0,0 +1,25 @@
+package ch.nuth.zhaw.exbox;
+
+/**
+ * Provides the functionality to determine the solution of a hanoi puzzle.
+ */
+public class HanoiServer implements CommandExecutor {
+    @Override
+    public String execute(String command) throws Exception {
+        int count = Integer.parseInt(command);
+        return moveDisks(count, 'A', 'B', 'C');
+    }
+
+    public String moveDisks(int count, char sourcePole, char restPole, char destinationPole) {
+        String start = "";
+        String mid = String.format("Move disk %d from %s to %s", count, sourcePole, destinationPole);
+        String end = "";
+
+        if (count > 1) {
+            start = moveDisks(count - 1, sourcePole, destinationPole, restPole);
+            end = moveDisks(count - 1, restPole, sourcePole, destinationPole);
+        }
+
+        return String.join(System.lineSeparator(), start, mid, end).trim();
+    }
+}