用兩個棧實現一個隊列與用兩個隊列實現一個棧9

 用兩個棧實現一個隊列

public class Offer9 {

    public static void main(String[] args) {
        CustomQueue<Integer> customQueue = new CustomQueue();
        customQueue.add(0);
        customQueue.add(1);
        customQueue.add(2);
        customQueue.add(3);

        customQueue.delete();
        customQueue.add(4);
        customQueue.add(5);
        customQueue.delete();
        customQueue.delete();
    }
}

class CustomQueue<T> {

    Stack<T> stackAdd = new Stack<>();

    Stack<T> stackDel = new Stack<>();

    public T add(T element) {
        return stackAdd.push(element);
    }

    public T delete() {
        if (stackDel.empty()) {
            if (!stackAdd.empty()) {
                while (!stackAdd.empty()) {
                    stackDel.push(stackAdd.pop());
                }
                return stackDel.pop();
            }
        } else {
            return stackDel.pop();
        }
        return null;
    }
}

用兩個隊列實現一個棧

public class Offer9 {

    public static void main(String[] args) {
        CustomStack<Integer> customStack = new CustomStack();

        customStack.add(1);
        customStack.add(2);
        customStack.add(3);
        customStack.add(4);

        customStack.delete();
        customStack.delete();

        customStack.add(5);
        customStack.add(6);
        customStack.delete();
    }
}

class CustomStack<T> {

    Queue<T> queue1 = new LinkedList<>();

    Queue<T> queue2 = new LinkedList<>();

    public boolean add(T element) {
        if (!queue2.isEmpty()) {
            return queue2.add(element);
        } else {
            return queue1.add(element);
        }
    }

    public T delete() {
        if (!queue2.isEmpty()) {
            while (!queue2.isEmpty()) {
                if (queue2.size() == 1) {
                    break;
                }
                queue1.offer(queue2.poll());
            }
            return queue2.poll();
        }
        if (!queue1.isEmpty()) {
            while (!queue1.isEmpty()) {
                if (queue1.size() == 1) {
                    break;
                }
                queue2.offer(queue1.poll());
            }
            return queue1.poll();
        }
        return null;
    }
}