Algorithm
Problem Name: 507. Perfect Number
A perfect number is a positive integer that is equal to the sum of its positive divisors, excluding the number itself. A divisor of an integer x is an integer that can divide x evenly.
Given an integer n, return true if n is a perfect number, otherwise return false.
Example 1:
Input: num = 28 Output: true Explanation: 28 = 1 + 2 + 4 + 7 + 14 1, 2, 4, 7, and 14 are all divisors of 28.
Example 2:
Input: num = 7 Output: false
Constraints:
1 <= num <= 108
Code Examples
#1 Code Example with Java Programming
Code -
Java Programming
class Solution {
public boolean checkPerfectNumber(int num) {
if (num == 1) {
return false;
}
return getDivisorSum(num) == num;
}
private int getDivisorSum(int num) {
int sum = 0;
for (int i = 2; i < = Math.sqrt(num); i++) {
if (num % i == 0) {
sum += i + num / i;
}
}
return sum + 1;
}
}
Input
num = 28
Output
true
#2 Code Example with Javascript Programming
Code -
Javascript Programming
const checkPerfectNumber = function(num) {
if (num === 1) return false;
return chk(num);
};
function chk(num) {
let min = 2;
let max = Math.ceil(Math.sqrt(num));
const res = [1];
for (let i = min; i < = max; i++) {
if (Number.isInteger(num / i) && res.indexOf(i) === -1) {
res.push(i, num / i);
}
}
if (res.reduce((ac, el) => ac + el, 0) === num) {
return true;
} else {
return false;
}
}
Input
num = 28
Output
true
#3 Code Example with Python Programming
Code -
Python Programming
class Solution:
def checkPerfectNumber(self, num):
"""
:type num: int
:rtype: bool
"""
sm, div =1, 2
while div**2<=num:
if num%div==0: sm+=div+(num//div)
div+=1
return sm==num and div>2
Input
num = 7
Output
false
#4 Code Example with C# Programming
Code -
C# Programming
namespace LeetCode
{
public class _0507_PerfectNumber
{
public bool CheckPerfectNumber(int num)
{
int[] primes = new int[] { 2, 3, 5, 7, 13, 17, 19, 31 };
foreach (int prime in primes)
{
if (PN(prime) == num)
return true;
}
return false;
}
private int PN(int p)
{
return (1 << (p - 1)) * ((1 << p) - 1);
}
}
}
Input
num = 7
Output
false