Merge pull request #81 from 4ndrelim/branch-refactorDS

refactor: DisjointSet

docs/team/profiles.md

@@ -2,7 +2,7 @@
 
 | Name      | Description/About                                                 | Website (LinkedIn/GitHub/Personal)                                                                   | Contributions                                               |
 |-----------|-------------------------------------------------------------------|------------------------------------------------------------------------------------------------------|-------------------------------------------------------------|
-| Andre     | Aspiring ML engineer. Developing this with wonderful ex-students. | You can find me [here](https://4ndrelim.github.io)!                                                  | Team lead                                                   |
+| Andre     | Aspiring ML engineer. Developing this with wonderful ex-students. | You can find me [here](https://4ndrelim.github.io)                                                   | Team lead                                                   |
 | Kai Ting  | Likes algorithms and a committed TA!                              | [Linkedin](https://www.linkedin.com/in/kai-ting-ho-425181268/)                                       | Cool sorting and obscure trees! B-Trees, ORS..              |
 | Changxian | DevOps is right up his alley!                                     | ...                                                                                                  | Hashing variants! BTS DevOps - configure Gradle & workflows |
 | Shu Heng  | Interested in ML, aspiring researcher.                            | No website but here's my [Linkedin](https://www.linkedin.com/in/yeoshuheng), please give me a job :< | CS Fundamentals! Stacks and queues! RB-tree.                |

src/main/java/dataStructures/disjointSet/quickFind/DisjointSet.java

@@ -7,6 +7,7 @@
 
 /**
  * Implementation of quick-find structure; Turns a list of objects into a data structure that supports union operations
+ * Note DS structure is not suited with duplicate elements!
  *
  * @param <T> generic type of object to be stored
  */
@@ -33,6 +34,19 @@ public DisjointSet(List<T> objects) {
         }
     }
 
+    /**
+     * Constructor to initialize Disjoint Set with a known array of objects.
+     * @param objects
+     */
+    public DisjointSet(T[] objects) {
+        identifier = new HashMap<>();
+        int size = objects.length;
+        for (int i = 0; i < size; i++) {
+            // internally, component identity is tracked with integers
+            identifier.put(objects[i], identifier.size()); // each obj initialize with a unique identity using size;
+        }
+    }
+
     public int size() {
         return identifier.size();
     }

src/main/java/dataStructures/disjointSet/weightedUnion/DisjointSet.java

@@ -10,6 +10,7 @@
  * Turns a list of objects into a data structure that supports union operations.
  * <p>
  * Note that implementation below includes path compression. Refer to README for more details
+ * Note DS structure is not suited with duplicate elements!
  *
  * @param <T> generic type of object to be stored
  */
@@ -39,6 +40,20 @@ public DisjointSet(List<T> objects) {
         }
     }
 
+    /**
+     * Constructor to initialize Disjoint Set structure with a known array of objects.
+     * @param objects
+     */
+    public DisjointSet(T[] objects) {
+        parents = new HashMap<>();
+        size = new HashMap<>();
+        for (int i = 0; i < objects.length; i++) {
+            T obj = objects[i];
+            parents.put(obj, obj); // initially, every object forms a tree, with itself as the root
+            size.put(obj, 1); // each tree has size 1 at the start
+        }
+    }
+
     /**
      * Internal helper method to find the root (identifier) of an object. Note that path compression has been included.
      * A point of concern might be performing path compression would require updating the sizes tracked by each node

src/test/java/dataStructures/disjointSet/quickFind/DisjointSetTest.java

@@ -24,6 +24,16 @@ public void construct_shouldCorrectlyInitializeNonEmpty() {
         Assert.assertFalse(ds.find("andre", "kai ting"));
     }
 
+    @Test
+    public void construct_shouldCorrectlyInitializeNonEmptyArray() {
+        String[] lst = new String[] { "andre", "chang xian", "jun neng", "kai ting", "shu heng" };
+
+        DisjointSet<String> ds = new DisjointSet<>(lst);
+        Assert.assertEquals(ds.size(), 5);
+
+        Assert.assertFalse(ds.find("andre", "kai ting"));
+    }
+
     @Test
     public void find_shouldCorrectlyFindItself() {
         List<String> lst = Arrays.asList("andre", "chang xian", "jun neng");

src/test/java/dataStructures/disjointSet/weightedUnion/DisjointSetTest.java

@@ -24,6 +24,16 @@ public void construct_shouldCorrectlyInitializeNonEmpty() {
         Assert.assertFalse(ds.find("andre", "kai ting"));
     }
 
+    @Test
+    public void construct_shouldCorrectlyInitializeNonEmptyArray() {
+        String[] lst = new String[] { "andre", "chang xian", "jun neng", "kai ting", "shu heng" };
+
+        DisjointSet<String> ds = new DisjointSet<>(lst);
+        Assert.assertEquals(ds.size(), 5);
+
+        Assert.assertFalse(ds.find("andre", "kai ting"));
+    }
+
     @Test
     public void find_shouldCorrectlyFindItself() {
         List<String> lst = Arrays.asList("andre", "chang xian", "jun neng");