Hackerrank - Project Euler+ #002 - Even Fibonacci numbers

Hackerrank – Problem description

The problem description – Hackerrank.

Solution

We will calculate Fibonacci numbers sequence using known algorithm. If the next number is even, add it to the result sum. We end up calculations when the next Fibonacci number is greater than upper number constraint.

I created solution in:

Ruby

All solutions are also available on my GitHub profile.

Ruby

def fibonacci(n)
  fi = (1 + Math.sqrt(5)) / 2
  psi = 1 - fi
  return ((fi**n - psi**n) / Math.sqrt(5)).to_i
end

def sum_of_even_fibonacci(number)
  index = 3                   # at index % 3 == 0 there are always even fibonacci numbers
  result = 0
  num = fibonacci(index)
  while num <= number
    result += num
    index += 3
    num = fibonacci(index)
  end
  return result
end

def sum_of_even_fibonacci_naive(number)
  result = 0
  a = 0
  b = 1
  while b < number
    temp = a + b
    a = b
    b = temp
    result += a if a % 2 == 0
  end
  return result
end

gets.chomp.to_i.times do
  input = gets.chomp.to_i
  puts sum_of_even_fibonacci_naive(input)
end

def fibonacci(n)

fi = (1 + Math.sqrt(5)) / 2

psi = 1 - fi

return ((fi**n - psi**n) / Math.sqrt(5)).to_i

end

def sum_of_even_fibonacci(number)

index = 3 # at index % 3 == 0 there are always even fibonacci numbers

result = 0

num = fibonacci(index)

while num <= number

result += num

index += 3

num = fibonacci(index)

end

return result

end

def sum_of_even_fibonacci_naive(number)

result = 0

a = 0

b = 1

while b < number

temp = a + b

a = b

b = temp

result += a if a % 2 == 0

end

return result

end

gets.chomp.to_i.times do

input = gets.chomp.to_i

puts sum_of_even_fibonacci_naive(input)

end

Pavol Pidanič

I can count to 1023 with 10 fingers

Hackerrank – Project Euler+ #002 – Even Fibonacci numbers

Hackerrank – Problem description

Solution

Ruby

Leave a Reply Cancel reply