freeCodeCamp/curriculum/challenges/english/08-coding-interview-prep/project-euler/problem-3-largest-prime-factor.english.md

id, challengeType, isHidden, title, forumTopicId

id	challengeType	isHidden	title	forumTopicId
5900f36f1000cf542c50fe82	5	false	Problem 3: Largest prime factor	301952

Description

The prime factors of 13195 are 5, 7, 13 and 29.

What is the largest prime factor of the given number?

Instructions

Tests

tests:
  - text: <code>largestPrimeFactor(2)</code> should return a number.
    testString: assert(typeof largestPrimeFactor(2) === 'number');
  - text: <code>largestPrimeFactor(2)</code> should return 2.
    testString: assert.strictEqual(largestPrimeFactor(2), 2);
  - text: <code>largestPrimeFactor(3)</code> should return 3.
    testString: assert.strictEqual(largestPrimeFactor(3), 3);
  - text: <code>largestPrimeFactor(5)</code> should return 5.
    testString: assert.strictEqual(largestPrimeFactor(5), 5);
  - text: <code>largestPrimeFactor(7)</code> should return 7.
    testString: assert.strictEqual(largestPrimeFactor(7), 7);
  - text: <code>largestPrimeFactor(8)</code> should return 2.
    testString: assert.strictEqual(largestPrimeFactor(8), 2);
  - text: <code>largestPrimeFactor(13195)</code> should return 29.
    testString: assert.strictEqual(largestPrimeFactor(13195), 29);
  - text: <code>largestPrimeFactor(600851475143)</code> should return 6857.
    testString: assert.strictEqual(largestPrimeFactor(600851475143), 6857);

Challenge Seed

function largestPrimeFactor(number) {
  // Good luck!
  return true;
}

largestPrimeFactor(13195);

Solution

const largestPrimeFactor = (number) => {
  let largestFactor = number;

  for (let i = 2; i <= Math.sqrt(largestFactor); i++) {
    if (!(largestFactor % i)) {
      let factor = largestFactor / i;
      let candidate = largestPrimeFactor(factor);

      return i > candidate ? i : candidate;
    }
  }

  return largestFactor;
}