example-problems.md

Example Problems

These questions are good examples of what you may encounter on the coding challenge. You should read each question and try to solve them for yourself.

Some of these examples are harder than the problems you will encounter on the challenge, but the concepts are all relevant. You should understand the solutions to these problems.

Questions

Q1: Write a method, pow, that takes two (non-negative, integer) numbers, base and exponent and returns base raised to the exponent power. (No fair using Ruby's base ** exponent notation!).

Q2: Write a method, sum which takes an array of numbers and returns the sum of the numbers.

Q3: Write a method, is_prime?, that takes a number num and returns true if it is prime and false otherwise.

You may wish to use the modulo operation: 5 % 2 returns the remainder when dividing 5 by 2: 1. If num is divisible by i, then num % i == 0. (You would not be expected to already know about modulo for the challenge)

Q4: Using your is_prime? method, write a new method, primes that takes a (non-negative, integer) number max and returns an array of all prime numbers less than max.

Solutions

Q1: pow

def pow(base, exponent)
  result = 1

  i = 1
  while i <= exponent
    result = result * base
    i += 1
  end

  result
end

Q2: sum

def sum(nums)
  total = 0

  i = 0
  while i < nums.count
    total += nums[i]

    i += 1
  end

  # return total
  total
end

Q3: is_prime?

# Works for values greater than 1

def is_prime?(num)
  i = 2
  while i < num
    is_divisible = ((num % i) == 0)

    if is_divisible
      # divisor found; stop and return false!
      return false
    end

    i += 1
  end

  # no divisors found
  true
end

Q4: primes

def primes(max)
  primes_arr = []

  i = 2
  while i < max
    if is_prime?(i)
      # i is prime; add it to the array
      primes_arr << i
    end

    i += 1
  end

  # return primes_arr
  primes_arr
end