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64 lines
1.5 KiB
Markdown
64 lines
1.5 KiB
Markdown
# [507. Perfect Number](https://leetcode.com/problems/perfect-number/)
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## 题目
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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.
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Now, given an
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**integer**
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n, write a function that returns true when it is a perfect number and false when it is not.
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**Example**:
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```
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Input: 28
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Output: True
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Explanation: 28 = 1 + 2 + 4 + 7 + 14
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```
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**Note**: The input number **n** will not exceed 100,000,000. (1e8)
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## 题目大意
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对于一个 正整数，如果它和除了它自身以外的所有正因子之和相等，我们称它为“完美数”。给定一个 整数 n， 如果他是完美数，返回 True，否则返回 False
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## 解题思路
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- 给定一个整数，要求判断这个数是不是完美数。整数的取值范围小于 1e8 。
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- 简单题。按照题意描述，先获取这个整数的所有正因子，如果正因子的和等于原来这个数，那么它就是完美数。
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- 这一题也可以打表，1e8 以下的完美数其实并不多，就 5 个。
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## 代码
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```go
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package leetcode
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import "math"
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// 方法一
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func checkPerfectNumber(num int) bool {
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if num <= 1 {
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return false
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}
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sum, bound := 1, int(math.Sqrt(float64(num)))+1
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for i := 2; i < bound; i++ {
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if num%i != 0 {
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continue
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}
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corrDiv := num / i
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sum += corrDiv + i
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}
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return sum == num
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}
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// 方法二 打表
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func checkPerfectNumber_(num int) bool {
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return num == 6 || num == 28 || num == 496 || num == 8128 || num == 33550336
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}
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``` |