2019年的第一篇文章，作为一个程序员，从18年coding到了19年，真是太开心啦

/**
 * based on min-heap
 * @author haofan.whf
 * @version $Id: PriorityQueue.java, v 0.1 2018年12月31日 23:23 haofan.whf Exp $
 */
public class PriorityQueue {

    private int[] heap;

    private int lastEleIndex = 0;

    public PriorityQueue(int heapSize){
        this.heap = new int[heapSize + 1];
        this.heap[0] = Integer.MIN_VALUE;
    }

    public int length(){
        return this.heap.length;
    }

    public void append(int ele){
        this.lastEleIndex ++;
        if(lastEleIndex > this.length() - 1){
            throw new RuntimeException("too much elements");
        }
        this.heap[lastEleIndex] = ele;
        for (int i = lastEleIndex; i > 1; ) {
            int parentIndex = i / 2;
            if(this.heap[i] < this.heap[parentIndex]){
                this.swap(i, parentIndex);
            }
            i = parentIndex;
        }
    }

    public int pop(){
        if(this.heap.length == 1){
            throw new RuntimeException("heap is empty");
        }
        int popedKey = this.heap[1];
        this.heap[1] = this.heap[lastEleIndex];
        this.heap[lastEleIndex] = 0;
        lastEleIndex --;
        if(this.heap.length == 2){
            return popedKey;
        }

        for (int i = 1; i <= lastEleIndex / 2;) {
            int leftChildIndex = 2 * i;
            int rightChildIndex = 2 * i + 1;
            if(rightChildIndex > lastEleIndex){
                //means i only has left child
                if(this.heap[i] > this.heap[leftChildIndex]){
                    this.swap(i, leftChildIndex);
                    i = leftChildIndex;
                }else{
                    break;
                }
            }else{
                //means i only has left child and right child
                if(this.heap[leftChildIndex] > this.heap[rightChildIndex]){
                    if(this.heap[i] > this.heap[rightChildIndex]){
                        this.swap(i, rightChildIndex);
                        i = rightChildIndex;
                    }else{
                        break;
                    }
                }else{
                    if(this.heap[i] > this.heap[leftChildIndex]){
                        this.swap(i, leftChildIndex);
                        i = leftChildIndex;
                    }else{
                        break;
                    }
                }
            }
        }

        return popedKey;
    }

    //swap i and j
    private void swap(int i, int j){
        int temp = this.heap[i];
        this.heap[i] = this.heap[j];
        this.heap[j] = temp;
    }

    public int findMin(){
        if(this.heap.length == 1){
            throw new RuntimeException("heap is empty");
        }
        return heap[1];
    }

    public void checkRI(){
        if(this.heap.length <= 2){
            return;
        }
        for (int i = 1; i <= this.lastEleIndex / 2; i++) {
            if(heap[i] > heap[2 * i]){
                throw new RuntimeException("it's not a min-heap");
            }
            if(i * 2 + 1 <= this.lastEleIndex && heap[i] > heap[i * 2 + 1]){
                throw new RuntimeException("it's not a min-heap");
            }
        }
    }

    public String toString(){
        StringBuilder sb = new StringBuilder();
        for (int i = 1; i <= this.lastEleIndex; i++) {
            sb.append(this.heap[i] + ",");
        }
        return sb.toString();
    }

    public static void main(String args[]){
        PriorityQueue priorityQueue = new PriorityQueue(10);
        priorityQueue.append(3);
        priorityQueue.append(2);
        priorityQueue.append(1);
        priorityQueue.append(10);
        priorityQueue.append(4);
        priorityQueue.append(7);
        priorityQueue.append(8);
        priorityQueue.append(6);
        priorityQueue.checkRI();
        System.out.println(priorityQueue);

        Assert.assertEquals(priorityQueue.findMin(), 1);


        Assert.assertEquals(priorityQueue.findMin(), 1);
        Assert.assertEquals(priorityQueue.pop(), 1);
        Assert.assertEquals(priorityQueue.pop(), 2);
        Assert.assertEquals(priorityQueue.pop(), 3);
        System.out.println(priorityQueue);
        priorityQueue.checkRI();

    }
}