Merge pull request #14 from sir-gon/feature/problem0002

Problem 0002: solved.

src/problem0002.test.ts

@@ -0,0 +1,32 @@
+/**
+ * Even Fibonacci numbers
+ *
+ * https://projecteuler.net/problem=2
+ *
+ * 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 four million,
+ * find the sum of the even-valued terms.
+ */
+
+import logger from './logger';
+
+import { problem0002 } from './problem0002';
+
+describe('problem 0002', () => {
+  it('problem 0002 solution found', () => {
+    expect.assertions(1);
+
+    const solutionFound = 4613732;
+    const top = 4000000;
+
+    const calculated = problem0002(top);
+
+    logger.info(`PROBLEM 0002 solution found: ${calculated}`);
+
+    expect(calculated).toBe(solutionFound);
+  });
+});

src/problem0002.ts

@@ -0,0 +1,43 @@
+/**
+ * Even Fibonacci numbers
+ *
+ * https://projecteuler.net/problem=2
+ *
+ * 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 four million,
+ * find the sum of the even-valued terms.
+ */
+
+import logger from './logger';
+
+export function problem0002(_top: number) {
+  let i = 0;
+  let last1 = 1;
+  let last2 = 0;
+  let evenSum = 0;
+
+  let fibo = 0;
+  do {
+    fibo = last2 + last1;
+
+    logger.debug(`Fibonacci (${i}) = ${fibo}`);
+
+    if (fibo % 2 === 0) {
+      evenSum += fibo;
+    }
+
+    // next keys:
+    last2 = last1;
+    last1 = fibo;
+    i += 1;
+  } while (fibo < _top);
+
+  logger.info(`RESULT = ${evenSum}`);
+  return evenSum;
+}
+
+export default { problem0002 };