[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/lib/exercises/include/exercises/hackerrank/projecteuler/euler002.hpp

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+#pragma once
+
+namespace hackerrank::projecteuler {
+
+int euler002(int n);
+
+} // namespace hackerrank::projecteuler

src/lib/exercises/src/hackerrank/projecteuler/euler002.cpp

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+#include <exercises/hackerrank/projecteuler/euler002.hpp>
+
+/**
+ * @link Problem definition [[docs/hackerrank/projecteuler/euler002.md]]
+ */
+
+#include <algorithm>
+
+namespace hackerrank::projecteuler {
+
+int fibo_even_sum(int n) {
+  int total = 0;
+  int fibo = 0;
+  int fibo1 = 1;
+  int fibo2 = 1;
+
+  while (fibo1 + fibo2 < n) {
+    fibo = fibo1 + fibo2;
+    fibo1 = fibo2;
+    fibo2 = fibo;
+
+    if (fibo % 2 == 0) {
+      total += fibo;
+    }
+  }
+
+  return total;
+}
+
+int euler002(int n) { return fibo_even_sum(n); }
+
+} // namespace hackerrank::projecteuler

src/tests/unit/lib/hackerrank/projecteuler/euler002.test.cpp

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+#include <catch2/catch_test_macros.hpp>
+
+#include <exercises/hackerrank/projecteuler/euler002.hpp>
+#include <iostream>
+#include <vector>
+
+#include <filesystem>
+#include <fstream>
+#include <nlohmann/json.hpp>
+using json = nlohmann::json;
+
+TEST_CASE("euler002 JSON Test Cases",
+          "[hackerrank] [jsontestcase] [projecteuler]") {
+  std::filesystem::path cwd = std::filesystem::current_path();
+  std::string path =
+      cwd.string() +
+      "/unit/lib/hackerrank/projecteuler/euler002.testcases.json";
+
+  INFO("euler002 JSON test cases FILE: " << path);
+
+  std::ifstream f(path);
+  json data = json::parse(f);
+
+  for (auto testcase : data) {
+    int result = hackerrank::projecteuler::euler002(testcase["n"]);
+    CHECK(result == testcase["expected"]);
+  }
+}

src/tests/unit/lib/hackerrank/projecteuler/euler002.testcases.json

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+[
+  { "n": 10, "expected": 10 },
+  { "n": 100, "expected": 44 }
+]