Add cartesian product algorithm.

README.md

@@ -15,6 +15,7 @@
 
 * Math
   * [Fibonacci Number](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/math/fibonacci)
+  * [Cartesian Product](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/math/cartesian-product)
 
 ## Running Tests
 

src/algorithms/math/cartesian-product/__test__/cartesianProduct.test.js

@@ -0,0 +1,19 @@
+import cartesianProduct from '../cartesianProduct';
+
+describe('cartesianProduct', () => {
+  it('should return null if there is not enough info for calculation', () => {
+    const product1 = cartesianProduct([1], null);
+    const product2 = cartesianProduct([], null);
+
+    expect(product1).toBeNull();
+    expect(product2).toBeNull();
+  });
+
+  it('should calculate the product of two sets', () => {
+    const product1 = cartesianProduct([1], [1]);
+    const product2 = cartesianProduct([1, 2], [3, 5]);
+
+    expect(product1).toEqual([[1, 1]]);
+    expect(product2).toEqual([[1, 3], [1, 5], [2, 3], [2, 5]]);
+  });
+});

src/algorithms/math/cartesian-product/cartesian-product.js

@@ -1 +0,0 @@
-

src/algorithms/math/cartesian-product/cartesianProduct.js

@@ -0,0 +1,15 @@
+export default function cartesianProduct(setA, setB) {
+  if (!setA || !setB || !setA.length || !setB.length) {
+    return null;
+  }
+
+  const product = [];
+
+  for (let indexA = 0; indexA < setA.length; indexA += 1) {
+    for (let indexB = 0; indexB < setB.length; indexB += 1) {
+      product.push([setA[indexA], setB[indexB]]);
+    }
+  }
+
+  return product;
+}