用栈实现队列；用队列实现栈；

 

 

  1 package my_basic;
  2 
  3 import java.util.LinkedList;
  4 import java.util.Queue;
  5 import java.util.Stack;
  6 
  7 public class StackAndQueueConvert {
  8 
  9     /*利用栈结构实现队列结构*/
 10     public static class Stack2Queue{
 11         private Stack<Integer> stackPush;
 12         private Stack<Integer> stackPop;
 13         
 14         public Stack2Queue() {
 15             this.stackPush = new Stack<Integer>();
 16             this.stackPop = new Stack<Integer>();
 17         }
 18         
 19         public void push(int num) {
 20             stackPush.push(num);
 21         }
 22         public int peek() {
 23             if (stackPush.empty() && stackPop.empty()) {
 24                 throw new RuntimeException("Queue is empty!");
 25             }
 26             daoData();
 27             return stackPop.peek();
 28         }
 29         public int poll() {
 30             if (stackPush.empty() && stackPop.empty()) {
 31                 throw new RuntimeException("Queue is empty!");
 32             }
 33             daoData();
 34             return stackPop.pop();
 35         }
 36         
 37         public void daoData() {
 38             if (!stackPop.isEmpty()) {  //原则1： 一定要pop栈 空 才可以倒数据
 39                 return;
 40             }
 41             while (!stackPush.isEmpty()) {  //原则2：倒数据一定要倒完
 42                 stackPop.push(stackPush.pop());
 43             }
 44         }
 45     }
 46     
 47     /*利用队列结构实现栈结构*/
 48     public static class Queue2Stack{
 49         public Queue<Integer> data;
 50         public Queue<Integer> help;
 51         
 52         public Queue2Stack() {
 53             data = new LinkedList<>();
 54             help = new LinkedList<>();
 55         }
 56         
 57         public void push(int num) {
 58             data.add(num);
 59         }
 60         public int peek() {
 61             if (data.isEmpty()) {
 62                 throw new RuntimeException("stack is empty!");
 63             }
 64             while (data.size() > 1) {
 65                 help.add(data.poll());
 66             }
 67             int res = data.poll();
 68             help.add(res);
 69             swap();
 70             return res;
 71         }
 72         
 73 
 74         public int poll() {
 75             if (data.isEmpty()) {
 76                 throw new RuntimeException("stack is empty!");
 77             }
 78             while (data.size() > 1) {
 79                 help.add(data.poll());
 80             }
 81             int res = data.poll();
 82             swap();
 83             return res;
 84         }
 85         
 86         private void swap() {
 87             Queue<Integer> tmp = help;
 88             help = data;
 89             data = tmp;
 90         }
 91         
 92     }
 93     
 94     public static void main(String[] args) {
 95         Queue2Stack qStack = new Queue2Stack();
 96         qStack.push(1);
 97         qStack.push(2);
 98         qStack.push(3);
 99         
100         while (!qStack.data.isEmpty()) {
101             System.out.println(qStack.poll());
102         }    
103         
104         //stack2queue
105         Stack2Queue squeue = new Stack2Queue();
106         squeue.push(1);
107         squeue.push(2);
108         squeue.push(3);
109         int res = squeue.poll();
110         System.out.println(res);
111         squeue.push(4);
112         res = squeue.poll();
113         System.out.println(res);
114     }
115 
116 }
117

 

posted @ 2019-04-24 16:42  _luckyz  阅读(144)  评论(0)    收藏  举报