Missing numbers

Problems/Missing-Number/README.md

@@ -0,0 +1,27 @@
+# Missing-Number
+
+Create a function that takes an array of numbers between 1 and 10 (excluding one number) and returns the missing number.
+
+## Infos which are maybe needed
+
+- The array of numbers will be unsorted (not in order).
+- Only one number will be missing.
+
+## Documentation
+
+### Solution Idea
+
+Sum all numbers in the array together and subtract this number from 55 (The sum from 1 to 10).
+
+---
+
+### [Implementation](./solver.ts)
+
+Doing exactly this what the solution idea says.
+
+---
+
+### Information's
+
+This problem comes from the newsletter [Sloth Bytes](https://slothbytes.beehiiv.com).
+[Post](https://slothbytes.beehiiv.com/p/jit-compliation) from February 11, 2026.

Problems/Missing-Number/missing-number.test.ts

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+import { describe, expect, it } from "vitest";
+import missingNumber from "./solver";
+
+describe("Finds the missing number", () => {
+	it("should return 5 for the first number-row", () => {
+		expect(missingNumber([1, 2, 3, 4, 6, 7, 8, 9, 10])).toEqual(5);
+	});
+
+	it("should return 10 for the second number-row", () => {
+		expect(missingNumber([7, 2, 3, 6, 5, 9, 1, 4, 8])).toEqual(10);
+	});
+
+	it("should return 7 for the third number-row", () => {
+		expect(missingNumber([10, 5, 1, 2, 4, 6, 8, 3, 9])).toEqual(7);
+	});
+});

Problems/Missing-Number/solver.ts

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+import type { FixedArray } from "../../utilities/types/fixedArray";
+import type { IntRange } from "../../utilities/types/intRange";
+
+export default function missingNumber(array: FixedArray<IntRange<1, 11>, 9>): number {
+	return 55 - array.reduce((preVal, val) => preVal + val, 0);
+}

README.md

@@ -8,9 +8,9 @@ This repository is about solving coding-problems. It contains famous (or not tha
 
 ## Problems
 
-Solved: **24 problems**
+Solved: **25 problems**
 
-🟢 Easy: 18  
+🟢 Easy: 19  
 🟠 Medium: 5  
 🔴 Hard: 1
 
@@ -40,6 +40,7 @@ Solved: **24 problems**
 | [Day number of year](./Problems/Day-Number-Of-Year/README.md)                           | 🟢 Easy    |
 | [Remove the last vowel](./Problems/Remove-The-Last-Vowel/README.md)                     | 🟢 Easy    |
 | [Bingo Check](./Problems/Bingo-Check/README.md)                                         | 🟢 Easy    |
+| [Missing Number](./Problems/Missing-Number/README.md)                                   | 🟢 Easy    |
 
 <!-- PROBLEMS_END -->
 

utilities/types/intRange.ts

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+// Source - https://stackoverflow.com/a/39495173
+// Posted by AlexG, modified by community. See post 'Timeline' for change history
+// Retrieved 2026-03-14, License - CC BY-SA 4.0
+
+type Enumerate<N extends number, Acc extends number[] = []> = Acc["length"] extends N
+	? Acc[number]
+	: Enumerate<N, [...Acc, Acc["length"]]>;
+
+export type IntRange<F extends number, T extends number> = Exclude<Enumerate<T>, Enumerate<F>>;