232. 用栈实现队列

class MyQueue {

/** Initialize your data structure here. */
private final Deque input;
private final Deque outout;
private int size = 0;
public MyQueue() {
input = new ArrayDeque<>();
outout = new ArrayDeque<>();

}

/** Push element x to the back of queue. */
public void push(int x) {
input.push(x);
size++;
}

/** Removes the element from in front of queue and returns that element. */
public int pop() {
if (size == 0) return -1;
if (outout.isEmpty()) refresh();
size--;
return outout.pop();
}

private void refresh() {
while (!input.isEmpty()){
outout.push(input.pop());
}
}

/** Get the front element. */
public int peek() {
if (size == 0) return -1;
if (outout.isEmpty()) refresh();
return outout.peek();
}

/** Returns whether the queue is empty. */
public boolean empty() {
return size == 0;
}
}