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freeCodeCamp/curriculum/challenges/english/08-coding-interview-prep/project-euler/problem-2-even-fibonacci-numbers.english.md
Kristofer Koishigawa 6cfd0fc503 fix: improve Project Euler descriptions, challenge seeds, and test cases (#38016)
* fix: improve Project Euler descriptions and test case

Improve formatting of Project Euler test descriptions. Also add poker hands array and new test case for problem 54

* feat: add typeof tests and gave functions proper names for first 100 challenges

* fix: continue fixing test descriptions and adding "before test" sections

* fix: address review comments

* fix: adjust grids in 18 and 67 and fix some text that reference files rather than the given arrays

* fix: implement bug fixes and improvements from review

* fix: remove console.log statements from seed and solution
2020-02-28 06:39:47 -06:00

2.1 KiB

id, challengeType, title, forumTopicId
id challengeType title forumTopicId
5900f36e1000cf542c50fe81 5 Problem 2: Even Fibonacci Numbers 301838

Description

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.

Instructions

Tests

tests:
  - text: <code>fiboEvenSum(10)</code> should return a number.
    testString: assert(typeof fiboEvenSum(10) === 'number');
  - text: <code>fiboEvenSum(10)</code> should return 10.
    testString: assert.strictEqual(fiboEvenSum(10), 10);
  - text: <code>fiboEvenSum(60)</code> should return 44.
    testString: assert.strictEqual(fiboEvenSum(60), 44);
  - text: <code>fiboEvenSum(1000)</code> should return 798.
    testString: assert.strictEqual(fiboEvenSum(1000), 798);
  - text: <code>fiboEvenSum(100000)</code> should return 60696.
    testString: assert.strictEqual(fiboEvenSum(100000), 60696);
  - text: <code>fiboEvenSum(4000000)</code> should return 4613732.
    testString: assert.strictEqual(fiboEvenSum(4000000), 4613732);
  - text: Your function should return an <code>even</code> value.
    testString: assert.equal(fiboEvenSum(10) % 2 === 0, true);

Challenge Seed

function fiboEvenSum(n) {
  // You can do it!
  return true;
}

fiboEvenSum(10);

Solution

const fiboEvenSum = (number) => {
  if (number <= 1) {
    return 0;
  } else {
    let evenSum = 0, prevFibNum = 1, fibNum = 2; // According to problem description our Fibonacci series starts with 1, 2
    for (let i = 2; fibNum <= number; i++) {
      if (fibNum % 2 == 0) {
        evenSum += fibNum;
      }
      [prevFibNum, fibNum] = [fibNum, prevFibNum + fibNum];
    }
    return evenSum;
  }
}