feat(maths): finishes Factors

maths/factors.ts

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+/**
+ * @function FindFactors
+ * @description Find all the factors of a natural number.
+ * @param {number} num - A natural number.
+ * @return {Set<number>} - A set of all the factors of given natural number.
+ * @see https://en.wikipedia.org/wiki/Divisor
+ * @example FindFactors(1) = [1]
+ * @example FindFactors(4) = [1,2,4]
+ * @example FindFactors(16) = [1,3,5,15]
+ */
+export const FindFactors = (num: number): Set<number> => {
+    if (num <= 0 || !Number.isInteger(num)) {
+        throw new Error("Only natural numbers are supported.");
+    }
+
+    const res: Set<number> = new Set();
+    // Iterates from 1 to square root of num & pushes factors into the res set.
+    for (let i = 1; i * i <= num; i++) {
+        if (num % i === 0) {
+            res.add(i);
+
+            const sqrtFactor = Math.floor(num / i);
+            res.add(sqrtFactor);
+        }
+    }
+
+    return res;
+};

maths/test/factors.test.ts

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+import { FindFactors } from "../factors";
+
+describe("FindFactors", () => {
+    test.each([-890, -5.56, -7, 0, 0.73, 4.2, NaN, -Infinity, Infinity])(
+        "should throw an error for non natural number %d",
+        (num) => {
+            expect(() => FindFactors(num)).toThrowError(
+                "Only natural numbers are supported."
+            );
+        }
+    );
+
+    test.each([
+        [1, new Set([1])],
+        [2, new Set([1, 2])],
+        [4, new Set([1, 2, 4])],
+        [6, new Set([1, 2, 3, 6])],
+        [16, new Set([1, 2, 4, 8, 16])],
+    ])(
+        "of %i should return the correct set of its factors",
+        (num, expected) => {
+            expect(FindFactors(num)).toStrictEqual(expected);
+        }
+    );
+});