最小堆，最大堆

最小堆

package com.tools;

public class MinHeap {
    
    public int[] num;
    
    public MinHeap(int[] num){
        this.num = num;
        build();
    }
    
    //交换数据
    private void swap(int i , int j){
        int temp;
        temp = num[i];
        num[i] = num[j];
        num[j] = temp;
    }
    
    //初始化构造二叉堆
    private void build(){
        
        for(int i = 0 ; i <= num.length/2-1; i++){
            Heap(i);
        }
        
    }

    //对堆进行整理
    private void Heap(int index){
        
        int small = index;
        int left,right;
        left = (index+1)*2-1;
        right = (index+1)*2;
        if(left<num.length&&num[left]<num[index])
            small = left;
        if(right<num.length&&num[right]<num[small])
            small = right;
        if(small == index)
            return;
        swap(small, index);
        Heap(small);
    }
    
    public int GetRoot(){
        return num[0];
    }
    
    public void SetHeadValue(int value){
        num[0] = value;
        Heap(0);
    }
    
}

最大堆

package com.tools;

public class MaxHeap {

    public int[] num;
    
    public MaxHeap(int[] num){
        this.num = num;
        BuildHeap();
    }
    
    private void BuildHeap(){
        for(int i = num.length/2-1 ; i >=0 ;i--){
            Heap(i);
        }
    }
    
    private void swap(int i, int j){
        int temp;
        temp = num[i];
        num[i] = num[j];
        num[j] = temp;
    }
    //index = 2
    private void Heap(int index){
        int left,right;
        left = (index+1)*2-1;
        right = (index+1)*2;
        int max = index;
        
        if(left<num.length && num[left]>num[index])
            max = left;
        if(right<num.length && num[right]>num[max])
            max = right;
        
        if(index == max)
            return ;
        swap(max,index);
        Heap(max);
        
    }
    
    public int GetRoot(){
        return num[0];
    }
    public void SetHeadValue(int value) {
        num[0] = value;
        Heap(0);
    }
    
}

实现类

package com.algorithm05;

import java.util.Scanner;

import com.tools.MaxHeap;
import com.tools.MinHeap;


public class Algorithm40 {
    
    
    public static void main(String[] args) {
        
        int[] num = new int[]{5,2,1,4,8,12,3,100,2000,30,50};
        Scanner scanner = new Scanner(System.in);
        int k;
        k = scanner.nextInt();
        int[] topK = new int[k];
        //首先将数组中前k个数放入topk数组中。
        for(int i = 0 ; i < k ; i++){
            topK[i] = num[i];
        }
        //将topk数组转换为最小堆
        MinHeap minHeap = new MinHeap(topK);
        
        //前k个数据进入topk数组中，之后对数组中剩余数组进行最小堆的匹配
        for(int j = k ; j < num.length; j++){
            //如果数组中的值比topk最小的值还要小，则对其进行更换。并更新topk的数组的结构
            if(num[j]>minHeap.num[0])
            {
                minHeap.SetHeadValue(num[j]);
            }
        }
        
        ////前k个数据进入topk数组中，之后对数组中剩余数组进行最大堆的匹配
        MaxHeap maxHeap = new MaxHeap(topK);
        for(int j = k ; j < num.length ; j++){
            if(num[j]<maxHeap.num[0])
            {
                maxHeap.SetHeadValue(num[j]);
            }
        }
    }
    
}