algorithm: greatest common factor

Maths/GreatestCommonFactor.ts

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+/**
+ * @function GreatestCommonFactor
+ * @description Determine the greatest common factor of a group of numbers.
+ * @param {Number[]} nums - An array of numbers.
+ * @return {Number} - The greatest common factor.
+ * @see https://www.mathsisfun.com/greatest-common-factor.html
+ * @example GreatestCommonFactor(12, 8) = 4
+ * @example GreatestCommonFactor(3, 6) = 3
+ * @example GreatestCommonFactor(32, 16, 12) = 4
+ */
+
+export const binaryGCF = (a: number, b: number): number => {
+  if (!Number.isInteger(a) || !Number.isInteger(b) || a < 0 || b < 0) {
+    throw new Error("numbers must be natural to determine factors");
+  }
+
+  while (b) {
+    [a, b] = [b, a % b]
+  }
+  return a;
+}
+
+export const greatestCommonFactor = (nums: number[]): number => {
+  if (nums.length === 0) {
+    throw new Error("at least one number must be passed in");
+  }
+
+  return nums.reduce(binaryGCF);
+};

Maths/test/GreatestCommonFactor.test.ts

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+import { binaryGCF, greatestCommonFactor } from "../GreatestCommonFactor";
+
+describe("binaryGCF", () => {
+  test.each([[12, 8, 4], [1, 199, 1], [88, 40, 8], [288, 160, 32]])(
+    "of given two numbers is correct",
+    (numa, numb, expected) => {
+      expect(binaryGCF(numa, numb)).toBe(expected);
+    },
+  );
+
+  test("only whole numbers should be accepted", () => {
+    expect(() => binaryGCF(0.5, 0.8)).toThrowError(
+      "numbers must be natural to determine factors",
+    );
+  });
+
+  test("only positive numbers should be accepted", () => {
+    expect(() => binaryGCF(-2, 4)).toThrowError(
+      "numbers must be natural to determine factors",
+    );
+  });
+});
+
+describe("greatestCommonFactor", () => {
+  test.each([[[7], 7], [[12, 8], 4], [[1, 199], 1], [[88, 40, 32], 8], [[288, 160, 64], 32]])(
+    "of given list is correct",
+    (nums, expected) => {
+      expect(greatestCommonFactor(nums)).toBe(expected);
+    },
+  );
+
+  test("the list should consist of at least one number", () => {
+    expect(() => greatestCommonFactor([])).toThrowError(
+      "at least one number must be passed in",
+    );
+  });
+});