寫在最前面：刷點簡單的題水一水

leetcode【507】Perfect Number

We define the Perfect Number is a positive integer that is equal to the sum of all its positive divisors except itself.

Now, given an integer n, write a function that returns true when it is a perfect number and false when it is not.

Example:

Input: 28
Output: True
Explanation: 28 = 1 + 2 + 4 + 7 + 14

Note: The input number n will not exceed 100,000,000. (1e8)

題目很簡單，沒啥好說的，求下該數的因子，把自己去掉即可

import math


class Solution:
    def checkPerfectNumber(self, num):
        """
        :type num: int
        :rtype: bool
        """
        if num <= 1:
            return False
        rlist = []
        i = 1
        newnum = 0
        while i <= math.sqrt(num):
            if num % i == 0:
                a = num // i
                rlist.append(i)
                if (a != num) & (a != i):
                    rlist.append(a)
            i += 1
        for j in range(len(rlist)):
            newnum += rlist[j]
        if num == newnum:
            return True
        else:
            return False
 

放一段java的，思路是一樣的，具體細節你想怎麼寫就怎麼寫，從0開始算，還是從1開始，無所謂

class Solution {
    public boolean checkPerfectNumber(int num) {
        if(num <=1)
        	return false;
	int sum = 0;
	int top = (int) Math.sqrt(num);
	for(int i = 1;i <= top; i++) {
		if((num % i) ==0) {
			sum += i;
            if ((num / i) != i && (num / i) !=num)
                {sum += num /i;}
            }
		}
	return sum == num;
			
    }   
}
 

public class Solution {
    public boolean checkPerfectNumber(int num) {
        if(num <= 1) 
            return false;
        int sum = 1;
        int up = (int)Math.sqrt(num);
        for(int i = 2; i <= up; i++){
            if((num % i) == 0) {sum += i; sum += num / i;}
        }
        
        return sum == num;
    }
}

python和java來回切有時候會反應不過來...不過都是本地和leetcode除錯通過的，下面放一個本地的測試程式碼：

package Arithmetic;

public class checkPerfectNumber {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		checkPerfectNumber check = new checkPerfectNumber();
		check.checkPerfectNumber(28);
		System.out.println(check.checkPerfectNumber(28));
	}
	public boolean checkPerfectNumber(int num) {
        if(num <=1)
        	return false;
	int sum = 0;
	int top = (int) Math.sqrt(num);
	for(int i = 1;i <= top; i++) {
		if((num % i) ==0) {
			sum += i;
            if ((num / i) != i && (num / i) !=num)
                {sum += num /i;}
            }
		}
	System.out.println(sum);
	return sum == num;
			
    } 

}