feat: Adding lesson12 implementation of leetcode with stack by Yemi

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

@@ -1,12 +1,15 @@
 package com.codedifferently.lesson12;
 
 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;
+    int result[] = new int[] {0, 0};
+    while (head.next != null) {
+      if (head.val != head.next.val && head.val % 2 == 0) {
+        if (head.val > head.next.val) result[head.val % 2] += 1;
+        else result[head.next.val % 2] += 1;
+      }
+      head = head.next;
+    }
+    return (result[0] == result[1]) ? "Tie" : (result[0] > result[1] ? "Even" : "Odd");
   }
 }

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

@@ -1,6 +1,5 @@
 package com.codedifferently.lesson12;
 
-/** Implement the below Stack by providing code for the class methods. */
 public class Stack {
   private ListNode top;
 
@@ -9,18 +8,30 @@ public Stack() {
   }
 
   public void push(int value) {
-    // Your code here
+    ListNode newNode = new ListNode(value);
+    newNode.next = top;
+    top = newNode;
   }
 
   public int pop() {
-    return 0;
+    int topmostValue = 0;
+    if (isEmpty()) {
+      return Integer.parseInt(null);
+    } else {
+      topmostValue = top.val;
+      top = top.next;
+      return topmostValue;
+    }
   }
 
   public int peek() {
-    return 0;
+    if (isEmpty()) {
+      return Integer.parseInt(null);
+    }
+    return top.val;
   }
 
   public boolean isEmpty() {
-    return true;
+    return top == null;
   }
 }