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)
完数 = 他所有正除数(不包括他本身)之和
判断一个数是不是完数
C++(3ms):
1 class Solution { 2 public: 3 bool checkPerfectNumber(int num) { 4 if(num == 1) 5 return false ; 6 int sum = 1 ; 7 for(int i = 2; i <= sqrt(num) ; i++){ 8 if (num % i == 0){ 9 sum += i ; 10 sum += num/i ; 11 } 12 } 13 return sum == num ; 14 } 15 };
java(15ms):
1 class Solution { 2 public boolean checkPerfectNumber(int num) { 3 if(num == 1) 4 return false ; 5 int sum = 1 ; 6 for(int i = 2; i <= Math.sqrt(num) ; i++){ 7 if (num % i == 0){ 8 sum += i ; 9 sum += num/i ; 10 } 11 } 12 return sum == num ; 13 } 14 }