algorithm: check if integer is palindrome

Maths/isPalindromeIntegerNumber.js

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+/**
+ * @function isPalindromeIntegerNumber
+ * @param { Number } x
+ * @returns {boolean} - input integer is palindrome or not
+ *
+ * time complexity : O(log_10(N))
+ * space complexity : O(1)
+ */
+export function isPalindromeIntegerNumber (x) {
+  if (typeof x !== 'number') {
+    throw new TypeError('Input must be a integer number')
+  }
+  // check x is integer
+  if (!Number.isInteger(x)) {
+    return false
+  }
+
+  // if it has '-' it cannot be palindrome
+  if (x < 0) return false
+
+  // make x reverse
+  let reversed = 0
+  let num = x
+
+  while (num > 0) {
+    const lastDigit = num % 10
+    reversed = reversed * 10 + lastDigit
+    num = Math.floor(num / 10)
+  }
+
+  // compare origin x and reversed are same
+  return x === reversed
+}

Maths/test/isPalindromeIntegerNumber.test.js

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+import { isPalindromeIntegerNumber } from '../isPalindromeIntegerNumber'
+
+describe('isPalindromeIntegerNumber', () => {
+  it('expects to return true when length of input is 1', () => {
+    expect(isPalindromeIntegerNumber(6)).toEqual(true)
+  })
+
+  it('expects to return true when input is palindrome', () => {
+    expect(isPalindromeIntegerNumber(121)).toEqual(true)
+    expect(isPalindromeIntegerNumber(12321)).toEqual(true)
+    expect(isPalindromeIntegerNumber(1221)).toEqual(true)
+  })
+
+  it('expects to return false when input is not palindrome', () => {
+    expect(isPalindromeIntegerNumber(189)).toEqual(false)
+  })
+
+  it('expects to return false when input is minus', () => {
+    expect(isPalindromeIntegerNumber(-121)).toEqual(false)
+    expect(isPalindromeIntegerNumber(-12321)).toEqual(false)
+  })
+
+  it('expects to return false when input is not integer number', () => {
+    expect(isPalindromeIntegerNumber(123.456)).toEqual(false)
+  })
+
+  it('expects to throw error when input is not a number', () => {
+    expect(() => isPalindromeIntegerNumber(undefined)).toThrowError()
+    expect(() => isPalindromeIntegerNumber({ key: 'val' })).toThrowError()
+    expect(() => isPalindromeIntegerNumber([])).toThrowError()
+  })
+})