[Swift]LeetCode507. 完美數 | Perfect Number

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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)

---

對於一個 正整數，若是它和除了它自身之外的全部正因子之和相等，咱們稱它爲「完美數」。

給定一個 正整數 n， 若是他是完美數，返回 True，不然返回 False

 示例：

輸入: 28
輸出: True
解釋: 28 = 1 + 2 + 4 + 7 + 14

 注意:

輸入的數字 n 不會超過 100,000,000. (1e8)

---

 12ms

 1 class Solution {
 2     func checkPerfectNumber(_ num: Int) -> Bool {
 3         if num < 2
 4         {
 5             return false
 6         }
 7         let n:Int = Int(sqrt(Double(num)))
 8         if n < 2
 9         {
10             return false
11         }
12         var ans:Int = 1
13         for i in 2...n
14         {
15             if num % i == 0
16             {
17                 ans += i
18                 if num / i != i
19                 {
20                     ans += num / i
21                 }
22             }
23         }
24         return  ans == num
25     }
26 }

---

12ms

 1 class Solution {
 2     func checkPerfectNumber(_ num: Int) -> Bool {
 3         
 4         guard num > 1 else { return false }
 5         
 6         var sum = 0
 7         var i = 1
 8         while Double(i) <= sqrt(Double(num)) {
 9             let isDivisor = (num % i == 0)
10             if isDivisor {
11                 let d1 = i
12                 let d2 = num / i
13                 sum = sum + d1
14                 if d2 != num && d2 != d1 {
15                     sum = sum + d2
16                 }
17                 if sum > num { return false }
18             }
19             i = i + 1
20         }
21         let isPerfect = sum == num
22         return isPerfect    
23     }
24 }

---

16ms

1 class Solution {
2     func checkPerfectNumber(_ num: Int) -> Bool {
3         if num == 6 || num == 28 || num == 496 || num == 8128 || num == 33550336 {
4             return true
5         }
6         return false
7     }
8 }

---

20ms

 1 class Solution {
 2     func checkPerfectNumber(_ num: Int) -> Bool {
 3         if num <= 1 {
 4             return false
 5         }
 6         
 7         let value = sqrt(Double(num))
 8         if value.isNaN || value.isInfinite {
 9             return false
10         }
11         
12         let max = Int(value)
13         if max < 2 {
14             return false
15         }
16         
17         var tempValue: Int = 1
18         for index in 2 ... max {
19             if num % index == 0 {
20                 tempValue += index
21                 tempValue += num / index
22             }
23         }
24         
25         return tempValue == num
26     }
27 }

---

28ms

 1 class Solution {
 2     func f(_ num: Int) -> Bool {
 3         if (num <= 1) {
 4             return false
 5         }
 6         var a = 0
 7         var max_num = Int(sqrt(Double(num)))
 8         a += 1
 9         if (2 <= max_num){
10             for i in 2...max_num {
11                 if num % i == 0 {
12                     a += i
13                     if i != num / i {
14                         a += num / i
15                     }
16                 }
17             }
18         }
19         
20         return a == num
21     }
22     
23     
24     func checkPerfectNumber(_ num: Int) -> Bool {
25         return f(num)
26     }
27 }