Merge pull request #131 from MikeBeloborodov/8_kyu_sum_of_differences…

…_in_array

8 kyu sum of differences in array

8_kyu/sum_of_differences_in_array/README.md

@@ -0,0 +1,17 @@
+### Sum of differences in array
+
+https://www.codewars.com/kata/5b73fe9fb3d9776fbf00009e/
+
+Your task is to sum the differences between consecutive pairs in the array in descending order.
+
+## Example
+
+```
+[2, 1, 10]  -->  9
+```
+
+In descending order: `[10, 2, 1]`
+
+Sum: `(10 - 2) + (2 - 1) = 8 + 1 = 9`
+
+If the array is empty or the array has only one element the result should be `0` (`Nothing` in Haskell, `None` in Rust).

8_kyu/sum_of_differences_in_array/sum_of_differences_in_array.test.ts

@@ -0,0 +1,7 @@
+import { sumOfDifferences } from "./sum_of_differences_in_array";
+
+describe("test cases", () => {
+  it("should return 9", () => expect(sumOfDifferences([1, 2, 10])).toBe(9));
+  it("should return 2", () => expect(sumOfDifferences([-3, -2, -1])).toBe(2));
+  it("should return 0", () => expect(sumOfDifferences([])).toBe(0));
+});

8_kyu/sum_of_differences_in_array/sum_of_differences_in_array.ts

@@ -0,0 +1,8 @@
+export const sumOfDifferences = (arr: number[]): number => {
+  return [...arr]
+    .sort((a, b) => b - a)
+    .reduce(
+      (sum, next, indx, array) => (!indx ? 0 : sum + (array[indx - 1] - next)),
+      0,
+    );
+};

README.md

@@ -50,9 +50,9 @@ npm run push "$description"
 
 ### Katas solved
 
-`Total`: 133
+`Total`: 134
 \
-`8_kyu`: 43
+`8_kyu`: 44
 \
 `7_kyu`: 44
 \