牛客网剑指offer=＞排序

JZ29 最小的K个数

https://www.nowcoder.com/practice/6a296eb82cf844ca8539b57c23e6e9bf?tpId=13&&tqId=11182&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking

import java.util.ArrayList;
import java.util.Arrays;

public class GetLeastNumbers {
    public static void main(String[] args) {
        int[] input = {4,5,1,6,2,7,3,8};
        int k = 4;
        new GetLeastNumbers().GetLeastNumbers_Solution(input,k).forEach(tmp->{
            System.out.println(tmp);
        });
    }

    public ArrayList<Integer> GetLeastNumbers_Solution(int [] input, int k) {
        ArrayList<Integer> res = new ArrayList<>();
        if(k==0){
            return res;
        }
//        Arrays.sort(input);
        quickSort(input,0,input.length-1);
        for(int i=0;i<k;i++){
            res.add(input[i]);
        }
        return res;
    }

    //快速排序
    public void quickSort(int[] input,int l,int r){
        if(l<r){
            int key = input[l];
            int i = l;
            int j = r;
            while(i<j){
                while(i<j&&input[j]>=key){
                    j--;
                }
                if(i<j){
                    input[i] = input[j];
                    i++;
                }
                while(i<j&&input[i]<key){
                    i++;
                }
                if(i<j){
                    input[j] = input[i];
                    j--;
                }
            }
            input[i] = key;
            quickSort(input,l,i-1);
            quickSort(input,i+1,r);
        }
    }
}

JZ63 数据流中的中位数
->https://www.nowcoder.com/practice/9be0172896bd43948f8a32fb954e1be1?tpId=13&&tqId=11216&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking

import java.util.PriorityQueue;
import java.util.Comparator;

public class Solution {

    /*
    使用大小顶堆
    小顶堆队首为队列中最小的值，大顶堆相反
    因此我们可以在大顶堆中存放全部数字的前半部分，小顶堆中存放数组的后半部分
    */
    
    private int count = 0;//全部数字的数量
    private PriorityQueue<Integer> low = new PriorityQueue<>();//默认小顶堆
    private PriorityQueue<Integer> high = new PriorityQueue<>(new Comparator<Integer>() {
        @Override
        public int compare(Integer o1, Integer o2) {
            return o2.compareTo(o1); //return (02 < o1) ? -1 : ((o2 == o1) ? 0 : 1);
        }
    });
    
    public void Insert(Integer num) {
        count++;
        if((count&1)==1){//如果是奇数,我们在取中位数时候只需要取出大顶堆的堆顶元素，但是要防止num会比小顶堆中的数小
            if(!low.isEmpty()&&num>low.peek()){
                low.offer(num);
                num = low.poll();
            }
            high.offer(num);
        }else{
            if(!high.isEmpty()&&num<high.peek()){
                high.offer(num);
                num = high.poll();
            }
            low.offer(num);
        }
    }

    public Double GetMedian() {
        double res = 0;
        if((count&1)==1){
            res = high.peek();
        }else{
            res = (high.peek()+low.peek())/2.0;
        }
        return res;
    }


}