Leetcod——232. 用栈实现队列、225. 用队列实现栈

class MyStack {
    Queue queue;
    Queue queueTemp;

    public MyStack() {
        queue = new LinkedList<>();
        queueTemp = new LinkedList<>();
    }
    
    public void push(int x) {
        queue.add(x);
    }
    
    public int pop() {
        saveOne();
        int temp = queue.remove();
        recover();
        return temp;
    }
    
    public int top() {
        saveOne();
        int temp = queue.peek();
        queueTemp.add(queue.remove());
        recover();
        return temp;
    }
    
    public boolean empty() {
        return (queue.isEmpty()) ? true : false;
    }

    public void saveOne(){
        while(queue.size() > 1){
            queueTemp.add(queue.remove());
        }
    }

    public void recover(){
        while(!queueTemp.isEmpty()){
            queue.add(queueTemp.remove());
        }
    }
}

/**
 * Your MyStack object will be instantiated and called as such:
 * MyStack obj = new MyStack();
 * obj.push(x);
 * int param_2 = obj.pop();
 * int param_3 = obj.top();
 * boolean param_4 = obj.empty();
 */

class MyStack {

    Queue queue1; // 和栈中保持一样元素的队列
    Queue queue2; // 辅助队列

    /** Initialize your data structure here. */
    public MyStack() {
        queue1 = new LinkedList<>();
        queue2 = new LinkedList<>();
    }
    
    /** Push element x onto stack. */
    public void push(int x) {
        queue2.offer(x); // 先放在辅助队列中
        while (!queue1.isEmpty()){
            queue2.offer(queue1.poll());
        }
        Queue queueTemp;
        queueTemp = queue1;
        queue1 = queue2;
        queue2 = queueTemp; // 最后交换queue1和queue2，将元素都放到queue1中
    }
    
    /** Removes the element on top of the stack and returns that element. */
    public int pop() {
        return queue1.poll(); // 因为queue1中的元素和栈中的保持一致，所以这个和下面两个的操作只看queue1即可
    }
    
    /** Get the top element. */
    public int top() {
        return queue1.peek();
    }
    
    /** Returns whether the stack is empty. */
    public boolean empty() {
        return queue1.isEmpty();
    }
}

总结

这个没啥好说的。就是对行为的模拟，非常适合用来熟悉一下栈和队列的基本操作。