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1.概念：

队列：只允许在一端进行插入数据操作，在另一端进行删除数据操作的特殊线性表，队列具有先进先出FIFO(First In First Out) 入队列：进行插入操作的一端称为队尾（Tail/Rear） 出队列：进行删除操作的一端称为队头Head/Front）

 2.队列的方法：

接下来模拟实现上述方法:

 双向链表实现:

先创建最基本的成员变量和构造方法，内部类

public class MyQueue {//内部类static class ListNode{public int val;public ListNode prev;public ListNode next;public ListNode(int val) {this.val = val;}}public ListNode first;public ListNode last;public int useSize;}

实现offer方法

 public void offer(int val){ListNode node = new ListNode(val);if(isEmpty()) {first = last = node;}else{last.next = node;node.prev = last;last = last.next;}useSize++;}
public boolean isEmpty(){return useSize == 0;}

实现poll方法

public int poll(){if(isEmpty()){return -1;}else {int val = first.val;first = first.next;if(first != null){first.prev = null;}useSize--;return val;}}
public boolean isEmpty(){return useSize == 0;}

实现peek方法

public int peek(){if(isEmpty()){return -1;}else {int val = first.val;return val;}}public boolean isEmpty(){return useSize == 0;}

测试:

public class Test {//MyQueuepublic static void main(String[] args) {MyQueue myQueue = new MyQueue();myQueue.offer(1);myQueue.offer(2);myQueue.offer(3);myQueue.offer(4);System.out.println(myQueue.useSize);System.out.println(myQueue.peek());System.out.println(myQueue.poll());System.out.println(myQueue.peek());System.out.println(myQueue.useSize);}
}

用循环数组实现队列:

 

 先创建最基本的成员变量和构造方法

public class MyCircleQueue {public int front;public int rear;public int[] elem;public MyCircleQueue(int k) {elem = new int[k + 1];}
}

实现入队方法 

 public boolean enQueue(int val){if(isFull()){return false;}else {elem[rear] = val;rear = (rear + 1) % elem.length;return true;}}
public boolean isFull(){return front == (rear + 1) % elem.length;}

实现出队方法

public boolean deQueue(){if(isEmpty()){return false;}else {front = (front + 1) % elem.length;return true;}
}
public boolean isEmpty(){return front == rear;}

获得队头元素

//获得队列的头元素public int Front(){if(isEmpty()){return -1;}else{return elem[front];}}public boolean isEmpty(){return front == rear;}

测试:

public class Test {
//循环数组实现队列public static void main(String[] args) {MyCircleQueue myCircleQueue = new MyCircleQueue(10);myCircleQueue.enQueue(1);myCircleQueue.enQueue(2);myCircleQueue.enQueue(3);myCircleQueue.enQueue(4);System.out.println(myCircleQueue.Front());System.out.println(myCircleQueue.deQueue());System.out.println(myCircleQueue.Front());System.out.println(myCircleQueue.rear);}
}