队列：先进先出的一种思想，就和我们现实世界排队一样，先到的人先处理。
队列基本操作：长度，是否为空，是否为满，遍历显示，添加元素，获取对头元素
实现方式：数组，链表，两个栈
创建队列类，包含属性及方法
public class ArrayQueue { private int maxSize; private int front; private int rear; private int[] arr; //创建队列的构造器 public ArrayQueue(int arrMaxSize) { maxSize = arrMaxSize; arr = new int[maxSize]; front = -1;//指向队列头部，front指向队列头的前一个位置 rear = -1;//指向队列尾部 } //队列是否满了 public boolean isFull() { return rear == maxSize - 1; } //队列是否为空 public boolean isEmpty(){ return rear==front; } //往队列中添加数 public void add(int n){ //首先判断是否满了 if(isFull()){ return; } rear++; arr[rear]=n; } //获取队头的数据 public int get(){ //判断是否为空 if(isEmpty()){ System.out.println("队列为空！"); } front++; return arr[front]; } //遍历队列 public void show(){ if(isEmpty()){ System.out.println("队列为空！"); return; } for (int i=0;i<arr.length;i++){ System.out.printf("arr[%d]=%d\n",i,arr[i]); } } //获取队头的数据 public int head(){ if(isEmpty()){ throw new RuntimeException("队列空的，不能取值"); } return arr[front+1]; } } public class LinkedQueueTest { public static void main(String[] args) { LinkedQueue linkedQueue =new LinkedQueue(); linkedQueue.add("zico"); linkedQueue.add("DEAN"); linkedQueue.add("zion"); linkedQueue.add("loco"); linkedQueue.add("simon"); linkedQueue.add("gray"); linkedQueue.printQueue(); linkedQueue.peek(); linkedQueue.pop(); linkedQueue.printQueue(); linkedQueue.peek(); linkedQueue.length(); } } // 节点类 class Node { public String data; public Node next; // 构造器 public Node() { this.data = null; this.next = null; } } // 链表队列类 // 链表不指定长度 class LinkedQueue { public Node front; public Node rear; public int maxSize; // 构造函数 public LinkedQueue() { Node node = new Node(); front = rear = node; maxSize = 0; } // 队列是否为空 public boolean isEmpty() { //两种方式均可 //return front == rear; return front.next == null; } // 入队列 public void add(String name) { Node temp = new Node(); temp.data = name; rear.next = temp; rear = temp; maxSize++; } // 出队列 public void pop() { if (isEmpty()) { System.out.println("队列为空！"); return; } Node temp = front.next; System.out.println("出队列：" + temp.data); front.next = temp.next; if (rear == temp) { rear = front; } maxSize--; } // 队列长度 public void length() { System.out.println("队列长度：" + maxSize); } //遍历队列 public void printQueue() { for (Node current = front.next; current != null; current = current.next) { System.out.print(current.data + " "); } System.out.println(); } // 队列头元素 public void peek(){ System.out.println("头元素："+ front.next.data); } } import java.util.Stack; public class StackQueueTest { public static void main(String[] args) { // Your MyQueue object will be instantiated and called as such: MyQueue obj = new MyQueue(); obj.push(1); int param_2 = obj.pop(); System.out.println(param_2); obj.push(2); int param_3 = obj.peek(); System.out.println(param_3); boolean param_4 = obj.empty(); System.out.println(param_4); } } class MyQueue { Stack<Integer> stack1 = new Stack<>(); Stack<Integer> stack2 = new Stack<>(); /** * Initialize your data structure here. */ public MyQueue() { } /** * Push element x to the back of queue. */ public void push(int x) { stack1.push(x); } /** * Removes the element from in front of queue and returns that element. */ public int pop() { if (stack2.size() == 0) { while (!stack1.isEmpty()) { int temp = stack1.peek(); stack2.push(temp); stack1.pop(); } } int res = stack2.peek(); stack2.pop(); return res; } /** * Get the front element. */ public int peek() { if (stack2.size() == 0) { while (!stack1.isEmpty()) { int temp = stack1.peek(); stack2.push(temp); stack1.pop(); } } int res = stack2.peek(); return res; } /** * Returns whether the queue is empty. */ public boolean empty() { return stack1.isEmpty() &stack2.isEmpty(); } }小组队列
