栈和队列

用两个栈实现一个队列

import java.util.Stack;
public class StackToQueue {

    static Stack stack1 = new Stack();
    static Stack stack2 = new Stack();

    public static void push(int node){
        stack1.push(node);
    }
    public static int pop(){
        if (stack2.isEmpty()){
            while (!stack1.empty()){
                stack2.push(stack1.pop());

            }
        }
        return stack2.pop();
    }
}

用两个队列实现一个栈

import java.util.LinkedList;
import java.util.Queue;

public class QueueToStack {
    static Queue queue1 = new LinkedList<>();
    static Queue queue2 = new LinkedList<>();
    public static void main(String[] args) {
        push(1);
        push(2);
        push(3);
        pop();
        push(4);
        pop();
        pop();
    }
    public static void pop(){
        if (queue1.size() != 0){
            while(true) {
                if (queue1.size() == 1) {
                    System.out.println("POP"+queue1.remove());
                    break;
                }
                queue2.add(queue1.remove());
            }
        }else if(queue2.size() != 0){
            while(true) {
                if (queue2.size() == 1) {
                    System.out.println("POP"+queue2.remove());
                    break;
                }
                queue1.add(queue2.remove());
            }
        }

    }

    public static void push(int n){
        queue1.add(n);
        System.out.println("PUSH"+n);
    }
}