feat: adds David's Stack and Lesson for Lesson 12

Author: dxsmith244

lesson_12/structs_java/structs_app/src/main/java/com/codedifferently/lesson12/Lesson12.java

@@ -6,7 +6,30 @@ public class Lesson12 {
    * Provide the solution to LeetCode 3062 here:
    * https://github.com/yang-su2000/Leetcode-algorithm-practice/tree/master/3062-winner-of-the-linked-list-game
    */
-  public String gameResult(ListNode head) {
-    return null;
-  }
-}
+    public String gameResult(ListNode head) {
+        int oddPoints = 0;
+        int evenPoints = 0;
+        ListNode current = head;
+        
+        while (current != null && current.next != null) {
+            int evenValue = current.val;
+            int oddValue = current.next.val;
+            
+            if (evenValue > oddValue) {
+                evenPoints++;
+            } else if (oddValue > evenValue) {
+                oddPoints++;
+            }
+
+            current = current.next.next;
+        }
+        
+        if (evenPoints > oddPoints) {
+            return "Even";
+        } else if (oddPoints > evenPoints) {
+            return "Odd";
+        } else {
+            return "Tie";
+        }
+    }
+  }

lesson_12/structs_java/structs_app/src/main/java/com/codedifferently/lesson12/Stack.java

@@ -9,18 +9,29 @@ public Stack() {
   }
 
   public void push(int value) {
-    // Your code here
-  }
+     ListNode node = new ListNode(value);
+     node.next = top;
+     top = node;
+   }
 
-  public int pop() {
-    return 0;
-  }
+   public int pop() {
+     if (isEmpty()){
+       throw new IllegalStateException("Stack has no values");
+     }
+     int valToPop = top.val;
+     top = top.next;
+     return valToPop;
+   }
 
-  public int peek() {
-    return 0;
-  }
+   public int peek() {
+     if (isEmpty()){
+       throw new IllegalStateException("Stack has no values");
+     }
 
-  public boolean isEmpty() {
-    return true;
-  }
-}
+     return top.val;
+   }
+
+   public boolean isEmpty() {
+     return top == null;
+   }
+ }

lesson_12/structs_java/structs_app/src/test/java/com/codedifferently/lesson12/Lesson12Test.java

@@ -1,7 +1,6 @@
 package com.codedifferently.lesson12;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
-
 import org.junit.jupiter.api.Test;
 
 class Lesson12Test {

lesson_12/structs_java/structs_app/src/test/java/com/codedifferently/lesson12/StackTest.java

@@ -4,7 +4,6 @@
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
-
 import org.junit.jupiter.api.Test;
 
 class StackTest {