Merge pull request #155 from MikeBeloborodov/7_kyu_difference_of_squares

difference of squares

7_kyu/difference_of_squares/README.md

@@ -0,0 +1,5 @@
+### Difference Of Squares
+
+https://www.codewars.com/kata/558f9f51e85b46e9fa000025
+
+![description](./description.jpg "Description")

7_kyu/difference_of_squares/difference_of_squares.test.ts

@@ -0,0 +1,5 @@
+import { differenceOfSquares } from "./difference_of_squares";
+
+describe("test cases", () => {
+  it("should return 170", () => expect(differenceOfSquares(5)).toBe(170));
+});

7_kyu/difference_of_squares/difference_of_squares.ts

@@ -0,0 +1,16 @@
+export const differenceOfSquares = (n: number) => {
+  const squareOfTheSum = Math.pow(
+    Array(n)
+      .fill(1)
+      .map((_, index) => index + 1)
+      .reduce((sum, next) => sum + next, 0),
+    2,
+  );
+
+  const sumOfSquares = Array(n)
+    .fill(1)
+    .map((_, index) => Math.pow(index + 1, 2))
+    .reduce((sum, next) => sum + next, 0);
+
+  return squareOfTheSum - sumOfSquares;
+};

README.md

@@ -56,11 +56,11 @@ npm run push "$description"
 
 ### Katas solved
 
-`Total`: 157
+`Total`: 158
 \
 `8_kyu`: 51
 \
-`7_kyu`: 55
+`7_kyu`: 56
 \
 `6_kyu`: 38
 \