more challenges

Author: bowbahdoe

src/collections/challenges.md

@@ -6,3 +6,79 @@ Remember the rules for this are
 - Try not to give up until you've given it a solid attempt
 
 ## Challenge 1.
+
+Replace uses of the "concrete" collection types (`ArrayList`, `HashMap`, `HashSet`)
+in the following code with the corresponding collection interfaces.
+
+You want to keep the calls like `new ArrayList` - only change how variables are typed.
+
+```java,editable
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+class Main {
+    void main() {
+        ArrayList<String> jedi = new ArrayList<>();
+        jedi.add("Luke");
+        jedi.add("Anakin");
+        jedi.add("Qui-Gon");
+        jedi.add("Obi-Wan");
+
+        HashSet<String> sith = new HashSet<>();
+        sith.add("Palpatine");
+
+        HashMap<String, String> winningMatchups 
+            = new HashMap<>();
+        winningMatchups.put("Anakin", "Palpatine");
+        winningMatchups.put("Obi-Wan", "Jar-Jar");
+
+        for (var j : jedi) {
+            IO.println(j + " is a jedi");
+
+            var matchup = winningMatchups.get(j);
+            if (matchup != null) {
+                if (sith.contains(matchup)) {
+                    IO.println(j + " would win against " + matchup);
+                }
+                else {
+                    IO.println(j + " would win against " + matchup + " (but they aren't sith)");
+                }
+            }
+
+        }
+    }
+}
+```
+
+## Challenge 2.
+
+Call `methodB` using the array returned from `methodA`.
+
+```java
+class Main {
+    String[] methodA() {
+        return new String[] {
+            "Chewbacca",
+            "Attichitcuk",
+            "Mallatobuck",
+            "Lumpawaroo"
+        }
+    }
+
+    void methodB(List<String> character) {
+        IO.println("Characters in the Star Wars Christmas Special:");
+        IO.println("----------------");
+        for (item : character) {
+            IO.println(item);
+        }
+    }
+
+    void main() {
+        // CODE HERE
+    }
+}
+```

src/multi_dimensional_arrays/challenges.md

@@ -88,10 +88,10 @@ void main() {
 
     IO.println(winnerB);
 
-    var winnerC = winner(new Character[][] {
-        new Character[] { "O", "X", "O" },
-        new Character[] { "O", "O", "X" },
-        new Character[] { "O", "X", "O" }
+    var winnerC = winner(new String[][] {
+        new String[] { "O", "X", "O" },
+        new String[] { "O", "O", "X" },
+        new String[] { "O", "X", "O" }
     });
 
     IO.println(winnerC);