add a solution for 206

fishercoder1534 · fishercoder1534 · commit d5901a38d4c2 · 2021-10-25T16:44:18.000-07:00
diff --git a/src/main/java/com/fishercoder/solutions/_206.java b/src/main/java/com/fishercoder/solutions/_206.java
@@ -34,4 +34,23 @@ ListNode reverse(ListNode head, ListNode newHead) {
         }
     }
 
+    public static class Solution3 {
+
+        /**
+         * I feel like using the variable called prev makes more sense to me on 10/25/2021
+         * since it's literally a previous node when we start reversing from the head of the list.
+         * Again, using a pen and paper to visualize the steps helps a lot to convert thoughts into code.
+         */
+        public ListNode reverseList(ListNode head) {
+            ListNode prev = null;
+            while (head != null) {
+                ListNode next = head.next;
+                head.next = prev;
+                prev = head;
+                head = next;
+            }
+            return prev;
+        }
+    }
+
 }
diff --git a/src/test/java/com/fishercoder/_206Test.java b/src/test/java/com/fishercoder/_206Test.java
@@ -11,12 +11,14 @@
 public class _206Test {
     private static _206.Solution1 solution1;
     private static _206.Solution2 solution2;
+    private static _206.Solution3 solution3;
     private static ListNode head;
 
     @BeforeClass
     public static void setup() {
         solution1 = new _206.Solution1();
         solution2 = new _206.Solution2();
+        solution3 = new _206.Solution3();
     }
 
     @Test
@@ -30,4 +32,10 @@ public void test2() {
         head = LinkedListUtils.contructLinkedList(new int[]{1, 2, 3, 4});
         assertEquals(LinkedListUtils.contructLinkedList(new int[]{4, 3, 2, 1}), solution2.reverseList(head));
     }
+
+    @Test
+    public void test3() {
+        head = LinkedListUtils.contructLinkedList(new int[]{1, 2, 3, 4});
+        assertEquals(LinkedListUtils.contructLinkedList(new int[]{4, 3, 2, 1}), solution3.reverseList(head));
+    }
 }
