add: 完美数

README.md

@@ -367,6 +367,11 @@ LeetCode 与 LintCode 解题记录。此为个人练习仓库，代码中对重
   - LeetCode 560. 和为K的子数组 <https://leetcode-cn.com/problems/subarray-sum-equals-k/>
   - LintCode 838. 子数组和为K <https://www.lintcode.com/problem/subarray-sum-equals-k/description>
 
+- [完美数](src/math/perfect-number.js)
+
+  - LeetCode 507. 完美数 <https://leetcode-cn.com/problems/perfect-number/>
+  - LintCode 1199. 完美的数 <https://www.lintcode.com/problem/perfect-number/description>
+
 ## 堆
 
 - [超级丑数](src/stack/super-ugly-number.js)【未完成】

src/math/perfect-number.js

@@ -0,0 +1,16 @@
+const pn = (p) => { // 欧几里得-欧拉定理
+  return (1 << (p - 1)) * ((1 << p) - 1)
+}
+
+/**
+ * @param {number} num
+ * @return {boolean}
+ */
+export const checkPerfectNumber = function (num) {
+  const primes = [2, 3, 5, 7, 13, 17, 19, 31]
+  for (const prime of primes) {
+    if (pn(prime) === num) return true
+  }
+
+  return false
+}

test/math/perfect-number.test.js

@@ -0,0 +1,6 @@
+import { checkPerfectNumber } from '../../src/math/perfect-number'
+
+test('完美数', () => {
+  expect(checkPerfectNumber(28)).toBe(true)
+  expect(checkPerfectNumber(2)).toBe(false)
+})