[Hacker Rank]: Project Euler #2: Even Fibonacci numbers solved ✓

Author: Gonzalo Diaz

docs/hackerrank/projecteuler/euler002.md

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+# [Even Fibonacci numbers](https://www.hackerrank.com/contests/projecteuler/challenges/euler002)
+
+- Difficulty: #easy
+- Category: #ProjectEuler+
+
+Each new term in the Fibonacci sequence is generated by adding the previous two terms.
+By starting with $ 1 $ and $ 2 $, the first $ 10 $ terms will be:
+
+$$ 1, 2, 3, 5, 8, 13, 21, 34, 55, 89 $$
+
+By considering the terms in the Fibonacci sequence whose values do not exceed
+$ N $, find the sum of the even-valued terms.
+
+## 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 $
+- $ 10 \leq N \leq 4 × 10^{16} $
+
+## Output Format
+
+Print the required answer for each test case.
+
+## Sample Input 0
+
+```text
+2
+10
+100
+```
+
+## Sample Output 0
+
+```text
+10
+44
+```
+
+## Explanation 0
+
+- For $ N = 10 $, we have $ \{2, 8\} $, sum is $ 10 $.
+
+- For $ N = 100 $, we have $ \{2, 8, 34 \} $, sum is $ 44 $.

src/hackerrank/projecteuler/euler002.test.ts

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+import { describe, expect, it } from '@jest/globals';
+import { logger as console } from '../../logger';
+
+import { euler002 } from './euler002';
+
+describe('euler002', () => {
+  it('euler002 Test case 0', () => {
+    expect.assertions(2);
+
+    const tests = [
+      { n: 10, answer: 10 },
+      { n: 100, answer: 44 }
+    ];
+
+    tests.forEach((test) => {
+      const calculated = euler002(test.n);
+      console.log(`euler002(${test.n}) solution found: ${test.answer}`);
+      expect(calculated).toStrictEqual(test.answer);
+    });
+  });
+});

src/hackerrank/projecteuler/euler002.ts

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+/**
+ * @link Problem definition [[docs/hackerrank/projecteuler/euler001.md]]
+ */
+
+export function fibo_even_sum(n: number): number {
+  let total = 0;
+  let fibo = 0;
+  let fibo1 = 1;
+  let fibo2 = 1;
+
+  while (fibo1 + fibo2 < n) {
+    fibo = fibo1 + fibo2;
+    fibo1 = fibo2;
+    fibo2 = fibo;
+
+    if (fibo % 2 == 0) {
+      total += fibo;
+    }
+  }
+
+  return total;
+}
+
+// Function to find the sum of all multiples of a and b below n
+export function euler002(n: number): number {
+  return fibo_even_sum(n);
+}