feat: add greatest common divisor algorithm

Maths/GreatestCommonDivisor.js

@@ -0,0 +1,23 @@
+/**
+ * @function greatestCommonDivisor
+ * @description Finds the greatest common divisor (GCD) of two integers
+ *   using the Euclidean algorithm.
+ * @param {number} a - First positive integer
+ * @param {number} b - Second positive integer
+ * @returns {number} - The GCD of a and b
+ * @see https://en.wikipedia.org/wiki/Greatest_common_divisor
+ * @example greatestCommonDivisor(12, 8) => 4
+ * @example greatestCommonDivisor(100, 75) => 25
+ * @example greatestCommonDivisor(7, 5) => 1
+ */
+const greatestCommonDivisor = (a, b) => {
+  if (!Number.isInteger(a) || !Number.isInteger(b) || a < 1 || b < 1) {
+    throw new TypeError('Both inputs must be positive integers')
+  }
+  while (b !== 0) {
+    ;[a, b] = [b, a % b]
+  }
+  return a
+}
+
+export { greatestCommonDivisor }

Maths/test/GreatestCommonDivisor.test.js

@@ -0,0 +1,43 @@
+import { greatestCommonDivisor } from '../GreatestCommonDivisor.js'
+
+describe('greatestCommonDivisor', () => {
+  test('greatestCommonDivisor(12, 8) returns 4', () => {
+    expect(greatestCommonDivisor(12, 8)).toBe(4)
+  })
+
+  test('greatestCommonDivisor(100, 75) returns 25', () => {
+    expect(greatestCommonDivisor(100, 75)).toBe(25)
+  })
+
+  test('greatestCommonDivisor(7, 5) returns 1', () => {
+    expect(greatestCommonDivisor(7, 5)).toBe(1)
+  })
+
+  test('greatestCommonDivisor(1, 1) returns 1', () => {
+    expect(greatestCommonDivisor(1, 1)).toBe(1)
+  })
+
+  test('greatestCommonDivisor of same numbers returns that number', () => {
+    expect(greatestCommonDivisor(5, 5)).toBe(5)
+  })
+
+  test('greatestCommonDivisor(48, 18) returns 6', () => {
+    expect(greatestCommonDivisor(48, 18)).toBe(6)
+  })
+
+  test('greatestCommonDivisor(100, 10) returns 10', () => {
+    expect(greatestCommonDivisor(100, 10)).toBe(10)
+  })
+
+  test('throws TypeError for zero input', () => {
+    expect(() => greatestCommonDivisor(0, 5)).toThrow(TypeError)
+  })
+
+  test('throws TypeError for negative input', () => {
+    expect(() => greatestCommonDivisor(-12, 8)).toThrow(TypeError)
+  })
+
+  test('throws TypeError for float input', () => {
+    expect(() => greatestCommonDivisor(12.5, 8)).toThrow(TypeError)
+  })
+})