changes made to lesson 12 stack and java.

Author: angie-3

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

@@ -7,6 +7,23 @@ 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;
+
+    ListNode current = head;
+    int evenTeam = 0;
+    int oddTeam = 0;
+    while (current != null) {
+      if (current.val < current.next.val) {
+        oddTeam++;
+      } else if (current.val > current.next.val) {
+        evenTeam++;
+      }
+      current = current.next.next;
+    }
+
+    if (evenTeam < oddTeam) {
+      return "oddTeamwins";
+    } else if (evenTeam > oddTeam) {
+      return "eveTeamwins";
+    } else return "tie";
   }
 }

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

@@ -9,18 +9,22 @@ public Stack() {
   }
 
   public void push(int value) {
-    // Your code here
+    ListNode first = new ListNode(value);
+    first.next = top;
+    top = first;
   }
 
   public int pop() {
-    return 0;
+    int value = top.val;
+    top = top.next;
+    return value;
   }
 
   public int peek() {
-    return 0;
+    return top.val;
   }
 
   public boolean isEmpty() {
-    return true;
+    return top == null;
   }
 }