[Hacker Rank]: Project Euler #1: Multiples of 3 and 5 solved ✓

docs/hackerrank/projecteuler/euler001.md

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+# [Multiples of 3 and 5](https://www.hackerrank.com/contests/projecteuler/challenges/euler001)
+
+- Difficulty: #easy
+- Category: #ProjectEuler+
+
+If we list all the natural numbers below $ 10 $ that are multiples of
+ $ 3 $ or $ 5 $, we get $ 3, 5, 6 $ and $ 9 $.
+ The sum of these multiples
+ is $ 23 $.
+
+Find the sum of all the multiples of $ 3 $ or $ 5 $ below $ N $.
+
+## Input Format
+
+First line contains $ T $ that denotes the number of test cases.
+This is followed by $ T $ lines, each containing an integer, $ N $.
+
+## Constraints
+
+- 1 $ \leq T \leq 10^5 $
+- 1 $ \leq N \leq 10^9 $
+
+## Output Format
+
+For each test case, print an integer that denotes the sum of all the multiples
+of $ 3 $ or $ 5 $ below $ N $.
+
+## Sample Input 0
+
+```text
+2
+10
+100
+```
+
+## Sample Output 0
+
+```text
+23
+2318
+```
+
+## Explanation 0
+
+For $ N = 10 $, if we list all the natural numbers below $ 10 $ that are
+ multiples of $ 3 $ or $ 5 $, we get $ 3, 5, 6 $ and $ 9 $.
+  The sum of these multiples is $ 23 $.
+
+Similarly for $ N = 100 $, we get $ 2318 $.

src/hackerrank/projecteuler/euler001.js

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+/**
+ * @link Problem definition [[docs/hackerrank/projecteuler/euler001.md]]
+ */
+
+// Function to return gcd of a and b
+export function gcd(a, b) {
+  if (a === 0) return b;
+  return gcd(b % a, a);
+}
+
+export function sumAp(n, d) {
+  // Number of terms
+  const _n = Math.floor(n / d);
+
+  return Math.floor((_n * (1 + _n) * d) / 2);
+}
+
+// Function to find the sum of all multiples of a and b below n
+export function euler001(a, b, n) {
+  // Since, we need the sum of multiples less than N
+  const _n = n - 1;
+  const lcm = Math.floor((a * b) / gcd(a, b));
+
+  return sumAp(_n, a) + sumAp(_n, b) - sumAp(_n, lcm);
+}

src/hackerrank/projecteuler/euler001.test.js

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+import { describe, expect, it } from '@jest/globals';
+import { logger as console } from '../../logger.js';
+
+import { euler001 } from './euler001.js';
+
+import TEST_CASES from './euler001.testcases.json';
+
+describe('euler001', () => {
+  it('euler001 JSON Test Cases', () => {
+    expect.assertions(3);
+
+    TEST_CASES.forEach((test) => {
+      const calculated = euler001(test.a, test.b, test.n);
+      console.log(
+        `euler001(${test.a}, ${test.b}, ${test.n}) solution found: ${test.answer}`
+      );
+
+      expect(calculated).toStrictEqual(test.answer);
+    });
+  });
+});

src/hackerrank/projecteuler/euler001.testcases.json

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+[
+  { "a": 3, "b": 5, "n": 10, "answer": 23 },
+  { "a": 3, "b": 5, "n": 100, "answer": 2318 },
+  { "a": 3, "b": 5, "n": 1000, "answer": 233168 }
+]