MaxHeap

import java.util.Arrays;
import java.util.Random;

/**
 * Created by jc6a on 2018/4/19.]
 * 二叉堆  堆中某个值总是不大于其父节点的值;堆总是一棵完全二叉树。(最大堆)
 */
public class MaxHeap {
    private int arr[];
    int count;
    private int capacity;
    public MaxHeap(int capacity){
        arr = new int[capacity+1];
        count = 0;
        this.capacity = capacity;
    }

    int size(){
        return count;
    }

    boolean isEmpty(){
        return count == 0;
    }

    void insert(int data){
        assert (count+1<=capacity);
        arr[count+1] = data;
        count++;
        shiftUp(count);
    }
    void shiftUp(int k){
        while(k>1 &&arr[k/2] 0);
        int max = arr[1];
        swap(arr,1,count);
        count --;
        shiftDown(1);
        return max;
    }
    void shiftDown(int k){
        while(k*2<=count){
            int j = 2*k;
            if(j+1<=count&&arr[j+1]>arr[j]){
                j+=1;
            }
            if(arr[k]>=arr[j]){
                break;
            }
            swap(arr,k,j);
            k = j;

        }
    }
    void swap(int arr[],int i,int j){
        int tmp = arr[i];
        arr[i] = arr[j];
        arr[j] = tmp;
    }