AA Code Evaluation : Update Organization.java with functional hire() method

java/com/aa/act/interview/org/Organization.java

@@ -1,13 +1,38 @@
 package com.aa.act.interview.org;
 
+import java.util.HashMap;
+import java.util.Map;
 import java.util.Optional;
+import java.util.concurrent.atomic.AtomicInteger;
 
 public abstract class Organization {
 
+    private AtomicInteger id = new AtomicInteger(); //emp id for new hires (assigned sequentially)
+    private Map<String, Position> positions = new HashMap<>();  //stores position obj by title for efficient lookup O(1)
     private Position root;
 
     public Organization() {
         root = createOrganization();
+        // single call to populate all the positions in the map during org creation/setup
+        populateAllPositions(root);
+    }
+
+    /**
+     * update map with all the positions in the org starting at the root
+     * (this function uses recursion but is still efficient as the computation is done only once at the beginning)
+     *
+     * @param position
+     */
+    private void populateAllPositions(Position position) {
+        Optional.ofNullable(position)
+                .ifPresent(p -> {
+                            positions.put(p.getTitle(), p);
+                            Optional.ofNullable(p.getDirectReports())
+                                    .ifPresent(drs ->
+                                            // add position(s) of direct report(s) recursively
+                                            drs.forEach(this::populateAllPositions));
+                        }
+                );
     }
 
     protected abstract Position createOrganization();
@@ -20,8 +45,14 @@ public Organization() {
      * @return the newly filled position or empty if no position has that title
      */
     public Optional<Position> hire(Name person, String title) {
-        //your code here
-        return Optional.empty();
+        return Optional.ofNullable(positions.get(title))
+                .map(position -> {
+                            position.setEmployee(Optional.of(new Employee(id.incrementAndGet(), person)));
+                            // update position in map to reflect hire, this isn't necessary but more of a nice-to-have
+                            positions.put(title, position);
+                            return position;
+                        }
+                );
     }
 
     @Override