LeetCode - Algorithms - 507. Perfect Number

Problem

507. Perfect Number

Java

my solution

There is one fact that odd perfect numbers are greater than \( 10^{1500} \) if exist. By Euclid–Euler theorem, there is a one-to-one relationship between even perfect numbers and Mersenne primes. Even perfect number have the form as \( 2^{p−1}(2^p−1) \).

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class Solution {
    public boolean checkPerfectNumber(int num) {
		if ((num & 1) == 1)
			return false;
		else {
			if (num == 0)
				return false;
			int n = num;
			int p = 0;
			for (; (n & 1) == 0; p++) {
				n = n >> 1;
			}
			int x = (2 << (p - 1)) * ((2 << p) - 1);
			return num == x;
		}
    }
}

Submission Detail

  • 156 / 156 test cases passed.
  • Runtime: 0 ms, faster than 100.00% of Java online submissions for Perfect Number.
  • Memory Usage: 37.7 MB, less than 23.24% of Java online submissions for Perfect Number.