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)
Related Topics:
Math
Similar Questions:
// OJ: https://leetcode.com/problems/perfect-number/
// Author: github.com/lzl124631x
// Time: O(sqrt(N))
// Space: O(1)
class Solution {
public:
bool checkPerfectNumber(int num) {
if (num <= 1) return false;
int sum = 0, end = sqrt(num);
for (int i = 1; i <= end; ++i) {
if (num % i) continue;
int j = num / i;
sum += i;
if (j != i && j != num) sum += j;
}
return sum == num;
}
};