用栈实现队列

class MyQueue {

    private LinkedList<Integer> stack1;
    private LinkedList<Integer> stack2;
    /** Initialize your data structure here. */
    public MyQueue() {
        stack1 = new LinkedList<Integer>();
        stack2 = new LinkedList<Integer>();
    }
    
    /** Push element x to the back of queue. */
    public void push(int x) {
        stack1.push(x);
    }
    
    private void trans (){
        for (int i=stack1.size();i>0;i--){
            stack2.push(stack1.pop());
        }
    }
    /** Removes the element from in front of queue and returns that element. */
    public int pop() {
        if (stack2.size()==0) trans();
        return stack2.pop();
    }
    
    /** Get the front element. */
    public int peek() {
        if (stack2.size()==0) trans();
        return stack2.peek();
    }
    
    /** Returns whether the queue is empty. */
    public boolean empty() {
        return stack1.size()==0 && stack2.size()==0;
    }
}