LeetCode-Implement Stack using Queues

Posted 2020-07-09 IncredibleThings

Implement the following operations of a stack using queues.

push(x) -- Push element x onto stack.
pop() -- Removes the element on top of the stack.
top() -- Get the top element.
empty() -- Return whether the stack is empty.
Notes:
You must use only standard operations of a queue -- which means only push to back, peek/pop from front, size, and is empty operations are valid.
Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).
Update (2015-06-11):
The class name of the Java function had been updated to MyStack instead of Stack.

class MyStack {
    List<Integer> list=new ArrayList<Integer>();
    
    // Push element x onto stack.
    public void push(int x) {
        list.add(x);
    }

    // Removes the element on top of the stack.
    public void pop() {
        int len=list.size();
        if(len>0){
            list.remove(len-1);
        }
    }

    // Get the top element.
    public int top() {
        int len=list.size();
        if(len>0){
            return list.get(len-1);
        }
        else{
            return 0;
        }
    }

    // Return whether the stack is empty.
    public boolean empty() {
        int len=list.size();
        if(len==0){
            return true;
        }
        else{
            return false;
        }
    }
}