feat: add strobogrammatic number algorithm

Maths/StrobogrammaticNumber.js

@@ -0,0 +1,29 @@
+/**
+ * @function isStrobogrammaticNumber
+ * @description A strobogrammatic number is a number whose numeral is
+ *   rotationally symmetric, so it appears the same when rotated 180 degrees.
+ *   Valid strobogrammatic digit pairs: 0↔0, 1↔1, 6↔9, 8↔8, 9↔6.
+ * @param {number} n - A positive integer
+ * @returns {boolean} - True if n is a strobogrammatic number, false otherwise
+ * @see https://en.wikipedia.org/wiki/Strobogrammatic_number
+ * @example isStrobogrammaticNumber(69) => true
+ * @example isStrobogrammaticNumber(818) => true
+ * @example isStrobogrammaticNumber(123) => false
+ */
+const isStrobogrammaticNumber = (n) => {
+  if (!Number.isInteger(n) || n < 0) {
+    throw new TypeError('Input must be a non-negative integer')
+  }
+  const map = { 0: '0', 1: '1', 6: '9', 8: '8', 9: '6' }
+  const str = String(n)
+  let left = 0
+  let right = str.length - 1
+  while (left <= right) {
+    if (map[str[left]] !== str[right]) return false
+    left++
+    right--
+  }
+  return true
+}
+
+export { isStrobogrammaticNumber }

Maths/test/StrobogrammaticNumber.test.js

@@ -0,0 +1,51 @@
+import { isStrobogrammaticNumber } from '../StrobogrammaticNumber.js'
+
+describe('isStrobogrammaticNumber', () => {
+  test('0 is strobogrammatic', () => {
+    expect(isStrobogrammaticNumber(0)).toBe(true)
+  })
+
+  test('1 is strobogrammatic', () => {
+    expect(isStrobogrammaticNumber(1)).toBe(true)
+  })
+
+  test('8 is strobogrammatic', () => {
+    expect(isStrobogrammaticNumber(8)).toBe(true)
+  })
+
+  test('69 is strobogrammatic', () => {
+    expect(isStrobogrammaticNumber(69)).toBe(true)
+  })
+
+  test('96 is strobogrammatic', () => {
+    expect(isStrobogrammaticNumber(96)).toBe(true)
+  })
+
+  test('818 is strobogrammatic', () => {
+    expect(isStrobogrammaticNumber(818)).toBe(true)
+  })
+
+  test('1001 is strobogrammatic', () => {
+    expect(isStrobogrammaticNumber(1001)).toBe(true)
+  })
+
+  test('123 is NOT strobogrammatic', () => {
+    expect(isStrobogrammaticNumber(123)).toBe(false)
+  })
+
+  test('2 is NOT strobogrammatic', () => {
+    expect(isStrobogrammaticNumber(2)).toBe(false)
+  })
+
+  test('100 is NOT strobogrammatic', () => {
+    expect(isStrobogrammaticNumber(100)).toBe(false)
+  })
+
+  test('throws TypeError for negative input', () => {
+    expect(() => isStrobogrammaticNumber(-69)).toThrow(TypeError)
+  })
+
+  test('throws TypeError for float input', () => {
+    expect(() => isStrobogrammaticNumber(6.9)).toThrow(TypeError)
+  })
+})