栈和队列的相互转化

//队列转栈
import java.util.LinkedList;
import java.util.Queue;
 
public class Queue_To_Stack {
    private static Queue<Integer> data ;  //原本的数据队列
    private static Queue<Integer> help ;    // 辅助队列
    
    public static void setStack(){  //定义一个栈
        data = new LinkedList<>();
        help = new LinkedList<>();
    }
    public static void push(int num){   //压入栈
        data.add(num);    
    }
    public static Integer pop(){    //出栈
        if(data.isEmpty()){
            throw new IllegalArgumentException("栈为空！") ;
        }
        while(data.size() > 1){   //全部出队列，直到最后一个
            help.add(data.poll()) ;
        }
        int res = data.poll();  //得到最后一个
        swpe();  // help  和   data交换
        return res ;
    }
    
    public static Integer peek(){   //栈顶元素
        if(data.isEmpty()){
            throw new IllegalArgumentException("栈为空！") ;
        }
        while(data.size() > 1){
            help.add(data.poll()) ;
        }
        int res = data.poll();
        data.add(res) ;
        swpe();
        return res ;
    }
    
    public static void swpe(){
        Queue<Integer> tmp = help;
        help = data;
        data = tmp;
    }
    public static void main(String[] args) {
        setStack();
        push(2);
        push(44);
        push(11);
        push(266);
        push(277);
        push(200);
        System.out.println(pop());
        System.out.println(peek());
    }
 
}

//栈转队列
import java.util.Stack;
 
public class Stack_To_Queue {
    private static  Stack<Integer> data;
    private static Stack<Integer> help ;
    
    public static void setQueue(){
        data = new Stack<>();
        help = new Stack<>();
    }
    public static void add(int num){
        data.push(num) ;
    }
    public static Integer poll(){
        if(data.isEmpty() && help.isEmpty()){
            throw new RuntimeException("队列为空!") ;
        }else{
            while(data.size()>0){
                help.push(data.pop()) ;
            }
            int res = help.pop();
            while(!help.isEmpty()){
                data.push(help.pop()) ;
            }
            return res ;
        }
    }
    public static Integer peek(){
        if(data.isEmpty() && help.isEmpty()){
            throw new RuntimeException("队列为空!") ;
        }else{
            while(data.size()>0){
                help.push(data.pop()) ;
            }
            int res = help.peek();
            while(!help.isEmpty()){
                data.push(help.pop()) ;
            }
            return res ;
        }
    }
    public static void main(String[] args) {
        setQueue();
        add(1);
        add(2);
        add(3);
        add(4);
        add(5);
        System.out.println(poll());
        System.out.println(poll());
        System.out.println(poll());
        System.out.println(poll());
        System.out.println(poll());
    }
}