代码随想录训练营第三十期|第十天|栈与队列part01|理论基础● 232.用栈实现队列● 225. 用队列实现栈

232. 用栈实现队列 - 力扣（LeetCode）

class MyQueue {
    Stack<Integer> in;
    Stack<Integer> out;

    public MyQueue() {
        in = new Stack<>();
        out = new Stack<>();
    }
    
    public void push(int x) {
        in.push(x);
    }
    
    public int pop() {
        move();
        return out.pop();
    }
    
    public int peek() {
        move();
        return out.peek();
    }
    
    public boolean empty() {
        return in.isEmpty() && out.isEmpty();
    }

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

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

225. 用队列实现栈 - 力扣（LeetCode）

class MyStack {
    Queue<Integer> queue1;
    Queue<Integer> queue2;

    public MyStack() {
        queue1 = new LinkedList<>();
        queue2 = new LinkedList<>();
    }
    
    public void push(int x) {
        queue2.offer(x);
        while (!queue1.isEmpty()) {
            queue2.offer(queue1.poll());
        }
        Queue<Integer> tmp;
        tmp = queue1;
        queue1 = queue2;
        queue2 = tmp;
    }
    
    public int pop() {
       return queue1.poll();
    }
    
    public int top() {
        return queue1.peek();
    }
    
    public boolean empty() {
        return queue1.isEmpty();
    }
}

/**
 * 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();
 */