leetcode 225

The reverse of leetcode 232. This time is using two stacks to simulate the operations of Queue.

We can also use just one stack to get the work done, however, I think, simple is the best, isn't it?

The draft paper:

import java.util.Stack;

public class MyQueue {
    private Stack<Integer> stackIn;
    private Stack<Integer> stackOut;

    public MyQueue() {
        stackIn = new Stack<>();
        stackOut = new Stack<>();
    }

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

    public int pop() {
        if (stackOut.empty()) {
            dumpStackInToOut();
        }

        return stackOut.pop();
    }

    public int peek() {
        if (stackOut.empty()) {
            dumpStackInToOut();
        }

        return stackOut.peek();
    }

    public boolean empty() {
        return stackIn.empty() && stackOut.empty();
    }

    public void dumpStackInToOut() {
        while (!stackIn.isEmpty()) {
            stackOut.push(stackIn.pop());
        }
    }

    public static void main(String[] args) {
        var queue = new MyQueue();
        queue.push(1);
        queue.push(2);
        System.out.println(queue.pop());
        queue.push(3);
        queue.push(4);
        System.out.println(queue.pop());
        System.out.println(queue.pop());
        System.out.println(queue.pop());
        System.out.println(queue.empty());
    }
}