带你了解Java数据结构和算法之队列

package com.ys.datastructure;
 
public class MyQueue {
    private Object[] queArray;
    //队列总大小
    private int maxSize;
    //前端
    private int front;
    //后端
    private int rear;
    //队列中元素的实际数目
    private int nItems;
     
    public MyQueue(int s){
        maxSize = s;
        queArray = new Object[maxSize];
        front = 0;
        rear = -1;
        nItems = 0;
    }
     
    //队列中新增数据
    public void insert(int value){
        if(isFull()){
            System.out.println("队列已满！！！");
        }else{
            //如果队列尾部指向顶了，那么循环回来，执行队列的第一个元素
            if(rear == maxSize -1){
                rear = -1;
            }
            //队尾指针加1，然后在队尾指针处插入新的数据
            queArray[++rear] = value;
            nItems++;
        }
    }
     
    //移除数据
    public Object remove(){
        Object removeValue = null ;
        if(!isEmpty()){
            removeValue = queArray[front];
            queArray[front] = null;
            front++;
            if(front == maxSize){
                front = 0;
            }
            nItems--;
            return removeValue;
        }
        return removeValue;
    }
     
    //查看对头数据
    public Object peekFront(){
        return queArray[front];
    }
     
     
    //判断队列是否满了
    public boolean isFull(){
        return (nItems == maxSize);
    }
     
    //判断队列是否为空
    public boolean isEmpty(){
        return (nItems ==0);
    }
     
    //返回队列的大小
    public int getSize(){
        return nItems;
    }
     
}

package com.ys.test;
 
import com.ys.datastructure.MyQueue;
 
public class MyQueueTest {
    public static void main(String[] args) {
        MyQueue queue = new MyQueue(3);
        queue.insert(1);
        queue.insert(2);
        queue.insert(3);//queArray数组数据为[1,2,3]
         
        System.out.println(queue.peekFront()); //1
        queue.remove();//queArray数组数据为[null,2,3]
        System.out.println(queue.peekFront()); //2
         
        queue.insert(4);//queArray数组数据为[4,2,3]
        queue.insert(5);//队列已满,queArray数组数据为[4,2,3]
    }
 
}

package com.ys.datastructure;
 
public class PriorityQue {
    private int maxSize;
    private int[] priQueArray;
    private int nItems;
     
    public PriorityQue(int s){
        maxSize = s;
        priQueArray = new int[maxSize];
        nItems = 0;
    }
     
    //插入数据
    public void insert(int value){
        int j;
        if(nItems == 0){
            priQueArray[nItems++] = value;
        }else{
            j = nItems -1;
            //选择的排序方法是插入排序，按照从大到小的顺序排列，越小的越在队列的顶端
            while(j >=0 && value > priQueArray[j]){
                priQueArray[j+1] = priQueArray[j];
                j--;
            }
            priQueArray[j+1] = value;
            nItems++;
        }
    }
     
    //移除数据,由于是按照大小排序的，所以移除数据我们指针向下移动
    //被移除的地方由于是int类型的，不能设置为null，这里的做法是设置为 -1
    public int remove(){
        int k = nItems -1;
        int value = priQueArray[k];
        priQueArray[k] = -1;//-1表示这个位置的数据被移除了
        nItems--;
        return value;
    }
     
    //查看优先级最高的元素
    public int peekMin(){
        return priQueArray[nItems-1];
    }
     
    //判断是否为空
    public boolean isEmpty(){
        return (nItems == 0);
    }
     
    //判断是否满了
    public boolean isFull(){
        return (nItems == maxSize);
    }
 
}