01 - Multiples of 3 or 5

Don't say so much, just coding...

Instruction

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Finish the solution so that it returns the sum of all the multiples of 3 or 5 below the number passed in.

Note: If the number is a multiple of both 3 and 5, only count it once. Also, if a number is negative, return 0(for languages that do have them)

Ruby

Init

  def solution(number)
    # put your solution here
  end

Sample Testing

  def test(actual, expected)
    Test.assert_equals(actual, expected)
  end
  
  Test.describe("example tests") do
    test(solution(10), 23)
    test(solution(20), 78)
    test(solution(200), 9168)
  end

Javascript

Init

  function solution(number){
    // put your solution here
  }

Sample Testing

  function test(n, expected) {
    let actual = solution(n)
    Test.assertEquals(actual, expected, `Expected ${expected}, got ${actual}`)
  }
  
  Test.describe("basic tests", function(){
    test(10,23)
  })

Thinking

想法(1): 從題目概述 natural numbers below 10 中開始模擬會出現的數字
想法(2): 計算兩者的加總，可以知道在算 3 or 5 的倍數
想法(3): 處理級距，需要從 1 ~ 參數 然後再來選取符合項目，並加總

圖片來源：Unsplash Jesus Kiteque

Hint & Reference

• Ruby
  • Ruby - Start a loop from 1
  • Ruby - apidock Select
  • Ruby - apidock Reduce
  • Ruby - Ruby ampersand colon shortcut
• JavaScript
  • JS - 4 Ways to Convert String to Character Array in JavaScript
  • JS - Convert Iterables to Array using Spread
  • JS - ES6 Arrow Functions Cheatsheet

Solution

Ruby

  # Solution 1
  def solution(number)
    [*1..number-1].select{ |n| n % 3 == 0 || n % 5 == 0}.reduce(&:+)
  end

  # Solution 2
  def solution(number)
    [*1...number].select{ |n| n % 3 == 0 || n % 5 == 0}.reduce(&:+)
  end

  # Solution 3
  def solution(number)
    (1...number).select{ |n| n % 3 == 0 || n % 5 == 0}.inject(&:+)
  end
  
  # Solution 4
  def solution(number)
    (1...number).select{ |n| (n % 5).zero? || (n % 3).zero?}.inject(:+)
  end

Javascript

  // Solution 1
  function solution(number){
    let sum = 0;

    for(i = 1; i < number; i++){
        if( i % 3 == 0 || i % 5 == 0){
          sum += i;
        }
    }
    return sum;
  }
  
  // Solution 2
  function solution(number){
    return number < 3 ? 0
      : [...Array(number).keys()]
        .map(k => (k % 3 === 0 || k % 5 === 0) ? k : 0 )
        .reduce((sum, num) => sum + num )
  }