LeetCode-507-Perfect Number

Perfect number

Title description: For a positive integer, if it is equal to the sum of all positive factors except itself, we call it a "perfect number".

Given an integer n, if it is a perfect number, return true, otherwise return false.

Please refer to LeetCode official website for example description.

Source: LeetCode
Link: https://leetcode-cn.com/problems/perfect-number/
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Solution one: Solution one

Add a Get NUM all positive factors (except itself) method calculateAllPrimeFactor , the return value is a List , returns the value of the sum of all the elements, it is judged whether or equal NUM , if equal, returns to true ; otherwise, return false .

The logic of as follows:

• First, declare a List to primeFactor ;
• If num is equal to 1, then directly return primeFactor ;
• Otherwise, add 1 to primeFactor ;
• If num less than 4, return primeFactor ;
• Traversing to and from the 2 NUM square root, if NUM be divisible thereof, this number and this number will be NUM added after the addition to the number primeFactor in.
• Finally return primeFactor .

import java.util.ArrayList;
import java.util.List;

/**
 * @Author: ck
 * @Date: 2021/10/3 11:43 上午
 */
public class LeetCode_507 {
    public static boolean checkPerfectNumber(int num) {
        List<Integer> primeFactor = calculateAllPrimeFactor(num);
        for (Integer integer : primeFactor) {
            num -= integer;
        }
        if (num == 0) {
            return true;
        }
        return false;
    }

    public static List<Integer> calculateAllPrimeFactor(int num) {
        List<Integer> primeFactor = new ArrayList<>();
        if (num == 1) {
            return primeFactor;
        }
        primeFactor.add(1);
        if (num < 4) {
            return primeFactor;
        }
        for (int i = 2; i <= Math.sqrt(num); i++) {
            if (num % i == 0) {
                primeFactor.add(i);
                primeFactor.add(num / i);
            }
        }
        return primeFactor;
    }

    public static void main(String[] args) {
        System.out.println(checkPerfectNumber(28));
    }
}

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