algorithm: check if integer is palindrome (#1177)

* feat: Add check number case * style: Fix formatting * fix: Remove number check part * feat: Create isPalindromeIntegerNumber * test: Add minus number case

Author: changicho

Maths/isPalindromeIntegerNumber.js

@@ -0,0 +1,33 @@
+/**
+ * @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()
+ })
+})