add: 快乐数

README.md

@@ -219,6 +219,11 @@ LeetCode 与 LintCode 解题记录。此为个人练习仓库，代码中对重
   - LeetCode 852. 山脉数组的峰顶索引 https://leetcode-cn.com/problems/peak-index-in-a-mountain-array/
   - LintCode 585. 山脉序列中的最大值 https://www.lintcode.com/problem/maximum-number-in-mountain-sequence/description
 
+- [快乐数](src/array/happy-number.js)
+
+  - LeetCode 202. 快乐数 https://leetcode-cn.com/problems/happy-number/
+  - LintCode 488. 快乐数 https://www.lintcode.com/problem/happy-number/description
+
 ## 栈
 
 - [最大矩阵](src/stack/maximal-rectangle.js)

src/array/happy-number.js

@@ -0,0 +1,14 @@
+/**
+ * @param {number} n
+ * @return {boolean}
+ */
+export const isHappy = function (n) {
+  const set = new Set()
+
+  while (n !== 1 && !set.has(n)) {
+    set.add(n)
+    n = n.toString().split('').reduce((a, b) => a + b * b, 0)
+  }
+
+  return n === 1
+}

test/array/happy-number.test.js

@@ -0,0 +1,6 @@
+import { isHappy } from '../../src/array/happy-number'
+
+test('快乐数', () => {
+  expect(isHappy(19)).toBe(true)
+  expect(isHappy(5)).toBe(false)
+})