feat: List 기반의 스택 push 메서드 구현

Author: ksundong

yoonexample/src/main/java/stack/ListStack.java

@@ -17,7 +17,10 @@ public boolean isEmpty() {
 
   @Override
   public void push(E data) {
-
+    Node<E> newNode = new Node<>(data);
+    newNode.next = this.head;
+    this.head = newNode;
+    this.size++;
   }
 
   @Override