Java版的数据结构——栈和队列

public static void main(String[] args) {
  Stack<Integer> s = new Stack();
  s.push(1);
  s.push(2);
  s.push(3);
  s.push(4);
  System.out.println(s.size());  // 获取栈中有效元素个数---> 4
  System.out.println(s.peek());  // 获取栈顶元素---> 4
  s.pop();  // 4出栈，栈中剩余1  2  3，栈顶元素为3
  System.out.println(s.pop());  // 3出栈，栈中剩余1 2  栈顶元素为3
  if(s.empty()){
    System.out.println("栈空");
 }else{
    System.out.println(s.size());
 }
}

import java.util.Arrays;
public class MyStack {
    //创建一个顺序栈
    public int[] elem;
    public int usedSize;
    public MyStack(){
        this.elem = new int[10];
    }
    //压栈
    public void push(int val){
        //首先判断栈是不是满了
        if(isFull()){
            //扩容
            elem = Arrays.copyOf(elem,elem.length * 2);
        }
        elem[usedSize++] = val;
    }
    //出栈
    public int pop(){
        if (isEmpty()){
            throw new EmptyException("栈是空的！");
        }
        return elem[--usedSize];
    }
    //查看栈顶
    public int peek(){
        if(isEmpty()){
            throw new EmptyException("栈是空的！");
        }
        return elem[usedSize - 1];
    }
    //判断栈是不是空了
    public boolean isEmpty(){
        return usedSize == 0;
    }
    //栈的大小
    public int size(){
        return usedSize;
    }
    //判断栈是不是满了
    public boolean isFull(){
        return usedSize == elem.length;
    }
}

// 递归方式
void printList(Node head){
  if(null != head){
    printList(head.next);
 }
  System.out.print(head.val + " ");
}

Stack<Node> s = new Stack<>();
  // 将链表中的结点保存在栈中
  Node cur = head;
  while(null != cur){
    s.push(cur);
    cur = cur.next;
  }
 // 将栈中的元素出栈
 while(!s.empty()){
    System.out.print(s.pop().val + " ");
 }

public static void main(String[] args) {
  Queue<Integer> q = new LinkedList<>();
  q.offer(1);
  q.offer(2);
  q.offer(3);
  q.offer(4);
  q.offer(5);          // 从队尾入队列
  System.out.println(q.size());
  System.out.println(q.peek());  // 获取队头元素
  q.poll();
  System.out.println(q.poll());  // 从队头出队列，并将删除的元素返回
  if(q.isEmpty()){
    System.out.println("队列空");
 }else{
    System.out.println(q.size());
 }
}

//链式队列
public class MyQueue {
    //首先创建结点，用内部类实现
    static class Node{
        public int val;
        public Node next;
        //构造方法
        public Node(int val){
            this.val = val;
        }
    }
    //有个队头指针和队尾指针
    public Node head;
    public Node last;
    //队列的大小
    public int usedSize;
    //入队
    public void offer(int val){
        Node node = new Node(val);
        if(head == null){//证明队列为空
            head = node;
            last = node;
        }else{//如果有元素了
            last.next = node;
            last = node;
        }
        usedSize++;
    }
    //出队
    public int poll() {
        //判断队列是否为空
        if (empty()) {
            throw new EmptyException("队列为空");//自定义异常类
        }
        int ret = head.val;
        head = head.next;
        if (head == null) {
            last = null;//只有一个结点时，那么last也要置空。因为如果last不置空，出队的结点还是有引用指向它，它就不会被gc回收
        }
        usedSize--;
        return ret;
    }
    //判断队列是否为空
    public boolean empty() {
        return usedSize == 0;
    }
    //查看队头元素
    public int peek(){
        //判断队列是否为空
        if (empty()) {
            throw new EmptyException("队列为空");//自定义异常类
        }
        return head.val;
    }
    //获得队列大小
    public int getUsedSizeize(){
        return usedSize;
    }
}

//循环队列
public class MyCircularQueue {
    private int elem[];
    private int front;//表示队列的头
    private int rear;//表示队列的尾
    //创建循环队列
    public MyCircularQueue(int k) {
        //如果是浪费空间，这里必须多加一个1
        this.elem = new int[k + 1];
    }
    //判断队列是否为满
    public boolean isFull() {
        return (rear + 1) % elem.length == front;
    }
    //入队列
    public boolean enQueue(int value) {
        //1. 检查是否队列是满的
        if (isFull()) {
            return false;
        }
        rear = (rear + 1) % elem.length;
        elem[rear] = value;
        return true;
    }
    //出队列
    public boolean deQueue() {
        //队列为空
        if (isEmpty()) {
            return false;
        }
        front = (front + 1) % elem.length;
        return true;
    }
    //得到队头元素
    public int Front() {
        if (isEmpty()) {
            return -1;
        }
        return elem[front];
    }
    //得到队尾元素
    public int Rear() {
        if(isEmpty()) {
            return -1;
        }
        int index = (rear == 0) ? elem.length - 1 : rear-1;
        return elem[index];
    }
    //判读队列是否为空
    public boolean isEmpty() {
        return front == rear;
    }
}