Issue williamfiset#133 solved together with test cases for toString() method in DoublyLinkedList data structure

Author: SamuelAl

src/main/java/com/williamfiset/algorithms/datastructures/linkedlist/DoublyLinkedList.java

@@ -287,7 +287,10 @@ public String toString() {
     sb.append("[ ");
     Node<T> trav = head;
     while (trav != null) {
-      sb.append(trav.data + ", ");
+      sb.append(trav.data);
+      if (trav.next != null) {
+        sb.append(", ");
+      }
       trav = trav.next;
     }
     sb.append(" ]");

src/test/java/com/williamfiset/algorithms/datastructures/linkedlist/LinkedListTest.java

@@ -309,6 +309,21 @@ public void testRandomizedIndexOf() {
     }
   }
 
+  @Test
+  public void testToString() {
+    DoublyLinkedList<String> strs = new DoublyLinkedList<>();
+    assertEquals(strs.toString(), "[  ]");
+    strs.add("a");
+    assertEquals(strs.toString(), "[ a ]");
+    strs.add("b");
+    assertEquals(strs.toString(), "[ a, b ]");
+    strs.add("c");
+    strs.add("d");
+    strs.add("e");
+    strs.add("f");
+    assertEquals(strs.toString(), "[ a, b, c, d, e, f ]");
+  }
+
   // Generate a list of random numbers
   static List<Integer> genRandList(int sz) {
     List<Integer> lst = new ArrayList<>(sz);