lfeat: lesson_12 and stack solutions in java

Author: txtran224

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

@@ -7,6 +7,22 @@ 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 even = 0;
+    int odd = 0;
+    while (head != null && head.next != null) {
+      if (head.val > head.next.val) {
+        even++;
+      } else {
+        odd++;
+      }
+      head = head.next.next;
+    }
+    if (even == odd) {
+      return ("Tie");
+    } else if (even > odd) {
+      return ("Even");
+    } else {
+      return ("Odd");
+    }
   }
 }

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

@@ -10,17 +10,23 @@ public Stack() {
 
   public void push(int value) {
     // Your code here
+    ListNode top2 = new ListNode(value);
+    top2.next = top;
+    top = top2;
   }
 
   public int pop() {
-    return 0;
+    int topvalue = top.val;
+    top = top.next;
+
+    return topvalue;
   }
 
   public int peek() {
-    return 0;
+    return top.val;
   }
 
   public boolean isEmpty() {
-    return true;
+    return top == null
   }
 }