add: 回文数

README.md

@@ -299,6 +299,11 @@ LeetCode 与 LintCode 解题记录。此为个人练习仓库，代码中对重
 
   - LeetCode 面试题 16.07. 最大数值 https://leetcode-cn.com/problems/maximum-lcci/
 
+- [回文数](src/math/palindrome-number.js)
+
+  - LeetCode 9. 回文数 https://leetcode-cn.com/problems/palindrome-number/
+  - LintCode 491. 回文数 https://www.lintcode.com/problem/palindrome-number/
+
 ## 堆
 
 - [超级丑数](src/stack/super-ugly-number.js)【未完成】

src/math/palindrome-number.js

@@ -0,0 +1,16 @@
+/**
+ * @param {number} x
+ * @return {boolean}
+ */
+export const isPalindrome = function (x) {
+  if (x < 0 || (x % 10 === 0 && x !== 0)) return false // 如果末尾数为0且不是0
+
+  let reverse = 0
+
+  while (reverse < x) {
+    reverse = reverse * 10 + x % 10
+    x = x / 10 | 0
+  }
+
+  return reverse === x || (reverse / 10 | 0) === x
+}

test/math/palindrome-number.test.js

@@ -0,0 +1,9 @@
+import { isPalindrome } from '../../src/math/palindrome-number'
+
+test('回文数', () => {
+  expect(isPalindrome(121)).toBe(true)
+  expect(isPalindrome(0)).toBe(true)
+  expect(isPalindrome(11)).toBe(true)
+  expect(isPalindrome(10)).toBe(false)
+  expect(isPalindrome(-121)).toBe(false)
+})