大根堆的实现

public static void swap(int[] arr , int i , int j){
    arr[i] =arr[i] ^arr[j];
    arr[j] =arr[i] ^arr[j];
    arr[i] =arr[i] ^arr[j];
}
//建一个大根堆
public static class MyMaxHeap{
    private int[] heap;
    private final int limit;
    private int heapSize;

    public MyMaxHeap(int limit){
        heap = new int[limit];
        this.limit  = limit;
        heapSize =0;
    }

    public boolean isEmpty(){
        return heapSize==0;
    }

    public boolean isFull(){
        return heapSize ==limit;
    }

    public void push(int value){
        if(heapSize == limit){
            throw new RuntimeException("heap is full");
        }
        heap[heapSize]  = value;
        heapInsert(heap ,  heapSize++);
    }

    public int pop(){
        int ans  = heap[0];
        swap(heap ,0 , --heapSize);
        heapify(heap , 0 ,heapSize);
        return ans;
    }
    //插入数据
    private void heapInsert(int[] arr , int index){
        while(arr[index]  >  arr[(index-1)/2]){
            swap(arr , index  ,(index-1)/2);
            index =  (index -1)/2;
        }
    }

    private void heapify(int[] arr ,int index ,int heapSize){
        int left =  index*2-1;
        while (left < heapSize){
         int largest = left+1 < heapSize && arr[left + 1]> arr[left] ? left +1  : left;
         largest = arr[largest] > arr[index]? largest :index;

         if(largest == index){
                break;
         }

            swap(arr ,largest , index);
            index =largest;
            left = index*2+1;
        }
    }
}