Implement Queue using Stacks leetcode

Implement the following operations of a queue using stacks.

• push(x) -- Push element x to the back of queue.
• pop() -- Removes the element from in front of queue.
• peek() -- Get the front element.
• empty() -- Return whether the queue is empty.

//方法1 push() O(n), pop() O(1), peek() O(1)
class MyQueue {
    Stack<Integer> stack = new Stack<Integer>();
    Stack<Integer> tem = new Stack<Integer>();
    public void push(int x) {
        if (stack.isEmpty()) {
            stack.push(x);
        } else {
            while (!stack.isEmpty()) {
                tem.push(stack.pop());
            }
            tem.push(x);
            while (!tem.isEmpty()) {
                stack.push(tem.pop());
            }
            
        }
    }
    public void pop() {
        stack.pop();
    }
    public int peek() {
        return stack.peek();
    }
    public boolean empty() {
        return stack.isEmpty();
    }
}
//方法2 push() O(1), pop() O(n), peek() O(n)
class MyQueue {
    private Stack<Integer> stack = new Stack<Integer>();
    private Stack<Integer> tem = new Stack<Integer>();
    public void push(int x) {
        stack.push(x);
    }
    public void pop() {
        int x = peek();
        tem.pop();
    }
    public int peek() {
        if (tem.isEmpty()) {
            while (!stack.isEmpty()) {
                tem.push(stack.pop());
            }
         }
         return tem.peek();
    }
    public boolean empty() {
        return stack.isEmpty() && tem.isEmpty();
    }
}