implement stack by arrayList

模拟一个arraylist, 就是 FI LO

public class Stack {    /*    * @param x: An integer    * @return: nothing    */    private Listlist = new ArrayList<>();

public void push(int x) {

// write your code here

list.add(x);

}

/*

* @return: nothing

*/

public void pop() {

// write your code here

list.remove(list.size() - 1);

}

/*

* @return: An integer

*/

public int top() {

// write your code here

return list.get(list.size() - 1);

}

/*

* @return: True if the stack is empty

*/

public boolean isEmpty() {

// write your code here

return list.size() <= 0;

}

}