2018-09-30 22:01:58 +00:00
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---
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id: 5900f36e1000cf542c50fe81
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title: 'Problem 2: Even Fibonacci Numbers'
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2020-11-27 18:02:05 +00:00
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challengeType: 5
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2019-08-05 16:17:33 +00:00
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forumTopicId: 301838
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2021-01-13 02:31:00 +00:00
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dashedName: problem-2-even-fibonacci-numbers
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2018-09-30 22:01:58 +00:00
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---
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2020-11-27 18:02:05 +00:00
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# --description--
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2020-02-28 12:39:47 +00:00
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2018-09-30 22:01:58 +00:00
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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:
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2020-02-28 12:39:47 +00:00
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2018-09-30 22:01:58 +00:00
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<div style='text-align: center;'>1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...</div>
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2020-02-28 12:39:47 +00:00
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2020-11-27 18:02:05 +00:00
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By considering the terms in the Fibonacci sequence whose values do not exceed `n`, find the sum of the even-valued terms.
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2020-07-26 17:09:46 +00:00
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2020-11-27 18:02:05 +00:00
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# --hints--
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2018-09-30 22:01:58 +00:00
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2020-11-27 18:02:05 +00:00
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`fiboEvenSum(10)` should return a number.
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2020-07-26 17:09:46 +00:00
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2020-11-27 18:02:05 +00:00
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```js
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assert(typeof fiboEvenSum(10) === 'number');
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```
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2018-09-30 22:01:58 +00:00
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2020-11-27 18:02:05 +00:00
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Your function should return an `even` value.
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2018-09-30 22:01:58 +00:00
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2020-11-27 18:02:05 +00:00
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```js
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assert.equal(fiboEvenSum(10) % 2 === 0, true);
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```
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2020-07-26 17:09:46 +00:00
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2020-11-27 18:02:05 +00:00
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Your function should sum the even-valued Fibonacci numbers: `fiboEvenSum(8)` should return 10.
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2018-09-30 22:01:58 +00:00
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2020-11-27 18:02:05 +00:00
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```js
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assert.strictEqual(fiboEvenSum(8), 10);
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2018-09-30 22:01:58 +00:00
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```
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2020-11-27 18:02:05 +00:00
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`fiboEvenSum(10)` should return 10.
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2018-09-30 22:01:58 +00:00
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2020-11-27 18:02:05 +00:00
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```js
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assert.strictEqual(fiboEvenSum(10), 10);
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```
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`fiboEvenSum(34)` should return 44.
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2020-07-26 17:09:46 +00:00
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2020-11-27 18:02:05 +00:00
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```js
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assert.strictEqual(fiboEvenSum(34), 44);
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```
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2018-09-30 22:01:58 +00:00
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2020-11-27 18:02:05 +00:00
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`fiboEvenSum(60)` should return 44.
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2018-09-30 22:01:58 +00:00
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```js
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2020-11-27 18:02:05 +00:00
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assert.strictEqual(fiboEvenSum(60), 44);
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```
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2020-09-15 19:31:21 +00:00
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2020-11-27 18:02:05 +00:00
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`fiboEvenSum(1000)` should return 798.
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```js
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assert.strictEqual(fiboEvenSum(1000), 798);
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2018-09-30 22:01:58 +00:00
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```
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2020-11-27 18:02:05 +00:00
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`fiboEvenSum(100000)` should return 60696.
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2018-09-30 22:01:58 +00:00
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2020-11-27 18:02:05 +00:00
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```js
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assert.strictEqual(fiboEvenSum(100000), 60696);
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```
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2018-09-30 22:01:58 +00:00
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2020-11-27 18:02:05 +00:00
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`fiboEvenSum(4000000)` should return 4613732.
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2018-09-30 22:01:58 +00:00
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2020-11-27 18:02:05 +00:00
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```js
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assert.strictEqual(fiboEvenSum(4000000), 4613732);
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```
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# --seed--
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## --seed-contents--
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```js
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function fiboEvenSum(n) {
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return true;
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}
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```
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# --solutions--
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2018-09-30 22:01:58 +00:00
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```js
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const fiboEvenSum = (number) => {
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2019-01-19 09:50:53 +00:00
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if (number <= 1) {
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return 0;
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} else {
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2020-07-26 17:09:46 +00:00
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let evenSum = 0,
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prevFibNum = 1,
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fibNum = 2; // According to problem description our Fibonacci series starts with 1, 2
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2020-02-07 16:09:35 +00:00
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for (let i = 2; fibNum <= number; i++) {
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if (fibNum % 2 == 0) {
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evenSum += fibNum;
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2018-09-30 22:01:58 +00:00
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}
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2020-02-07 16:09:35 +00:00
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[prevFibNum, fibNum] = [fibNum, prevFibNum + fibNum];
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}
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return evenSum;
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2019-01-19 09:50:53 +00:00
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}
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2020-07-26 17:09:46 +00:00
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};
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2018-09-30 22:01:58 +00:00
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```
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