leetcode 507. Perfect Number 完美数字

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)

题意很简单，直接计算即可

代码如下：

#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <string>
#include <climits>
#include <algorithm>
#include <sstream>
#include <functional>
#include <bitset>
#include <cmath>

using namespace std;

class Solution
{
public:
bool checkPerfectNumber(int num)
{
if (num == 1)
return false;

int sum = 1;
for (int i= 2; i <= (int)sqrt(num); i++)
{
if (num%i == 0)
{
sum += i;
if (i != num / i)
sum += num / i;
}
}
return sum == num;
}
};