feat: added Stack impl/ LeetCode 3062 finished in Java

Author: XavierCruz5106

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

@@ -7,6 +7,25 @@ public class Lesson12 {
    * https://github.com/yang-su2000/Leetcode-algorithm-practice/tree/master/3062-winner-of-the-linked-list-game
    */
   public String gameResult(ListNode head) {
-    return null;
+    int e_pts = 0;
+    int o_pts = 0;
+
+    ListNode curr = head;
+
+    while (curr != null) {
+      ListNode next = curr.next;
+      if (curr.val > next.val) {
+        e_pts++;
+      } else if (curr.val < next.val) {
+        o_pts++;
+      }
+      curr = next.next;
+    }
+
+    if (e_pts == o_pts) {
+      return "Tie";
+    }
+
+    return e_pts > o_pts ? "Even" : "Odd";
   }
 }

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;
+    if (isEmpty()) {
+      throw new IllegalStateException("Stack is empty");
+    }
+    int valToPop = top.val;
+    top = top.next;
+    return valToPop;
   }
 
   public int peek() {
-    return 0;
+    if (isEmpty()) {
+      throw new IllegalStateException("Stack is empty");
+    }
+
+    return top.val;
   }
 
   public boolean isEmpty() {
-    return true;
+    return top == null;
   }
 }