From 24c861fb8550f95c37f19c1d831150aaa6e75c39 Mon Sep 17 00:00:00 2001
From: Tcheumen <107006692+Tcheumen@users.noreply.github.com>
Date: Mon, 3 Jul 2023 19:01:28 +0200
Subject: [PATCH] feat: added binomial coefficient function and the
 corresponding test #10 (#141)

---
 maths/binomial_coefficient.ts           | 24 +++++++++++++++++
 maths/test/binomial_coefficient.test.ts | 34 +++++++++++++++++++++++++
 2 files changed, 58 insertions(+)
 create mode 100644 maths/binomial_coefficient.ts
 create mode 100644 maths/test/binomial_coefficient.test.ts

diff --git a/maths/binomial_coefficient.ts b/maths/binomial_coefficient.ts
new file mode 100644
index 00000000..cc522c3b
--- /dev/null
+++ b/maths/binomial_coefficient.ts
@@ -0,0 +1,24 @@
+import { Factorial } from "./factorial";
+/**
+ * @function BinomialCoefficient
+ * @description Calculate the binomial coefficient (n choose k) of two input numbers.
+ * @param {number} n - the total number of items
+ * @param {number} k - the number of items to be chosen
+ * @return {number} - Binomial coefficient (n choose k)
+ * @see https://en.wikipedia.org/wiki/Binomial_coefficient
+ * @example BinomialCoefficient(5, 2) = 10
+ * @example BinomialCoefficient(10, 3) = 120
+ * @example BinomialCoefficient(6, 0) = 1
+ */
+
+export const BinomialCoefficient = (n: number, k: number): number => {
+    // Check if k is larger than n or negative
+    if (k > n || k < 0) {
+        return 0;
+    }
+
+    // Calculate the binomial coefficient using the implemented factorial
+    const numerator = Factorial(n);
+    const denominator = Factorial(k) * Factorial(n - k);
+    return numerator / denominator;
+};
diff --git a/maths/test/binomial_coefficient.test.ts b/maths/test/binomial_coefficient.test.ts
new file mode 100644
index 00000000..ca677264
--- /dev/null
+++ b/maths/test/binomial_coefficient.test.ts
@@ -0,0 +1,34 @@
+import { BinomialCoefficient } from '../binomial_coefficient'; 
+
+describe('BinomialCoefficient', () => {
+    it('should calculate the correct binomial coefficient', () => {
+        // Test cases with expected results
+        const testCases: [number, number, number][] = [
+            [5, 2, 10],
+            [10, 3, 120],
+            [6, 0, 1],
+            [4, 4, 1],
+            [7, 5, 21],
+            [10, 10, 1],
+        ];
+
+        // Iterate through each test case and verify the result
+        testCases.forEach(([n, k, expected]) => {
+            const result = BinomialCoefficient(n, k);
+            expect(result).toEqual(expected);
+        });
+    });
+
+    it('should return 0 if k is larger than n or negative', () => {
+        const invalidCases: [number, number][] = [
+            [5, 6], // k is larger than n
+            [10, -3], // k is negative
+            [5, 10], // k is larger than n
+        ];
+
+        invalidCases.forEach(([n, k]) => {
+            const result = BinomialCoefficient(n, k);
+            expect(result).toEqual(0);
+        });
+    });
+});