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1. Find binary in input integer 1 The number of

2. Perfect number calculation

1. Find binary in input integer 1 The number of

Find input integers in binary 1 The number of _ Niuke Tiba _ Cattle from 【 Niuke Tiba 】 Collect high-frequency school recruitment pen interview questions from enterprises , With official explanation , Online Baidu Alibaba Tencent Netease and other Internet famous enterprises written interview simulation test practice , Discuss the classic test questions with Niu Ren , Improve your technical ability in an all-round way https://www.nowcoder.com/practice/1b46eb4cf3fa49b9965ac3c2c1caf5ad?tpId=37&&tqId=21285&rp=1&ru=/activity/oj&qru=/ta/huawei/question-ranking

① Topics and examples ：

 ② Method resolution ：

This problem is very similar to the one we brushed yesterday , Its purpose is to calculate the binary lower 1 The number of , Then we can use bitwise and 1 To calculate , Move the number to be calculated to the right one bit at a time , The result is 1, be count++;

However, it is also worth noting that the title emphasizes paying attention to multiple groups of input and output , So we will use scanner Medium scanner.hasNext() This method , Let's take a look at some of its instructions

This is a reference jdk1.8 Result . in other words , At the end of a set of data output , It doesn't stop the program process immediately , It will block the program first , Enter the next set of data . 

③ The code is as follows ：

import java.util.*;
public class demo4 {
    public static void main(String[]args){
        Scanner sc=new Scanner(System.in);
        while(sc.hasNext()){
            int n=sc.nextInt();
            int count=0;
            while(n!=0){
                if((n&1)==1){
                    count++;
                }
                n>>=1;
            }
            System.out.println(count);
        }
    }
}

2. Perfect number calculation

Perfect number calculation _ Niuke Tiba _ Cattle from 【 Niuke Tiba 】 Collect high-frequency school recruitment pen interview questions from enterprises , With official explanation , Online Baidu Alibaba Tencent Netease and other Internet famous enterprises written interview simulation test practice , Discuss the classic test questions with Niu Ren , Improve your technical ability in an all-round way https://www.nowcoder.com/practice/7299c12e6abb437c87ad3e712383ff84?tpId=37&&tqId=21279&rp=1&ru=/activity/oj&qru=/ta/huawei/question-ranking

① Topics and examples ：

 ② Method resolution ：

The meaning of this topic will not be explained too much , The problem is very simple , It's mainly about the divisor and （ Remove itself ） To judge . What we should pay attention to in this question is that when judging the divisor, we can choose from the range cut , Because the two are corresponding . And because it is not selected , So we can divide our relative divisor 1 Add it directly to the end to judge .

③ The code is as follows ：

import java.util.*;
public class Main {
    public static void main(String[]args){
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        int count=0;
        for(int i=2;i<=n;i++){
            if(isPerfectNum(i)){
                count++;
            }
        }System.out.println(count);
    }// Judge the divisor 
    public static boolean isPerfectNum(int i){
        int sum=0;
        for(int j=2;j<Math.sqrt(i);j++){
            if((i%j==0)){
                sum+=j+(i/j);
            }
        }
        if(i==sum+1){
            return true;
        }else{
            return false;
        }
    }
}