模板

用棧模擬佇列

class MyQueue {
    private Stack<Integer> in = new Stack<>();
    private Stack<Integer> out = new Stack<>();

    public void push(int x) {
        in.push(x);
    }

    public int pop() {
        in2out();
        return out.pop();
    }

    public int peek() {
        in2out();
        
 
return out.peek();
    }

    private void in2out() {
        if (out.isEmpty()) {
            while (!in.isEmpty()) {
                out.push(in.pop());
            }
        }
    }

    public boolean empty() {
        return in.isEmpty() && out.isEmpty();
    }
}

用佇列模擬棧

//一個棧
class MyStack {
    Queue
 
<Integer> queueA = new LinkedList<>();
    /** Initialize your data structure here. */
    public MyStack() {}
    
    /** Push element x onto stack. */
    public void push(int x) {
        int len = queueA.size();
        queueA.offer(x);
        for(int i=0;i<len;i++){
            queueA.offer(queueA.poll());
        }
    }
    
    
 
/** Removes the element on top of the stack and returns that element. */
    public int pop() {
        return queueA.poll();

    }
    
    /** Get the top element. */
    public int top() {
        return queueA.peek();
    }

    /** Returns whether the stack is empty. */
    public boolean empty() {
        return queueA.isEmpty();
    }
}