feat: add perfect number (#221)

* feat: add perfect numbers

* Optimize isPerfectNumber function and update tests

Author: ei-sugimoto

maths/perfect_number.ts

@@ -0,0 +1,27 @@
+/**
+ * @function isPerfectNumber
+ * @abstract A function to determine if a number is a perfect number
+ * @param {number} n
+ *
+ * @example console.log(isPerfectNumber(6)) => true
+ * @example console.log(isPerfectNumber(28)) => true
+ * @example console.log(isPerfectNumber(12))=> false
+ */
+
+export const isPerfectNumber = (n: number): boolean => {
+    if (n <= 0 || !Number.isInteger(n)) {
+        return false;
+    }
+    let sum = 1;
+    let sqrt = Math.sqrt(n);
+    for (let i = 2; i < sqrt; i++) {
+        if (n % i === 0) {
+            sum += i + n / i;
+        }
+    }
+    if (sqrt === Math.floor(sqrt)) {
+        sum += sqrt;
+    }
+
+    return sum === n;
+};

maths/test/perfect_numbers.test.ts

@@ -0,0 +1,18 @@
+import { isPerfectNumber } from "../perfect_number";
+
+describe('perfect Numbers tests', () => {
+  it.each([
+    [6, true],
+    [28, true],
+    [496, true],
+    [8128, true],
+    [12, false],
+    [42, false],
+    [100, false],
+    [0, false],
+    [-1, false],
+    [1.5, false],
+  ])('The return value of %i should be %s', (n, expectation) => {
+    expect(isPerfectNumber(n)).toBe(expectation);
+  });
+});