public class ArrayStack<E> implements Stack<E> {

Array<E> array;

public ArrayStack(int capacity) {

array = new Array<>(capacity);

}

public ArrayStack(){

array = new Array<>();

}

@Override

public int getSize() { // O(1)

return array.getSize();

}

@Override

public boolean isEmpty() { // O(1)

return array.isEmpty();

}

public int getCapacity() {

return array.getCapacity();

}

@Override

public void push(E e) { // O(1)

array.addLast(e);

}

@Override

public E pop() { // O(1) Average complexity

return array.removeLast();

}

@Override

public E peek() { // O(1) Average complexity

return array.getLast();

}

@Override

public String toString() {

StringBuilder res = new StringBuilder();

res.append("Stack: ");

res.append('[');

for (int i = 0; i < array.getSize(); i++) {

res.append(array.get(i));

if (i != array.getSize() - 1) {

res.append(", ");

}

}

res.append("] top");

return res.toString();

}

}

// 所有操作都是 O(1), 但是使用了 Array 作为容器，可能会触发 resize