diff --git a/Java/Ch 17. Hard/Q17_25_Word_Rectangle/WordGroup.java b/Java/Ch 17. Hard/Q17_25_Word_Rectangle/WordGroup.java
index adbd4bc6..7e39c58c 100644
--- a/Java/Ch 17. Hard/Q17_25_Word_Rectangle/WordGroup.java	
+++ b/Java/Ch 17. Hard/Q17_25_Word_Rectangle/WordGroup.java	
@@ -5,7 +5,7 @@
 
 /* A container for a group of words of the same length. */
 public class WordGroup {
-	private HashMap<String, Boolean> lookup = new HashMap<String, Boolean>();
+	private HashSet<String> lookup = new HashSet<String>();
     private ArrayList<String> group = new ArrayList<String>();
     
     public WordGroup() {
@@ -18,7 +18,7 @@ public boolean containsWord(String s) {
     
     public void addWord (String s) {
         group.add(s);
-        lookup.put(s, true);
+        lookup.put(s);
     }
     
     public int length() {