SPOJ 011 - Factorial

fctrl.rb

def z_naive(n)
  temp = 1
  num_zeroes = 0
  (2..n).each do |i|
    temp *= i
    while temp%10 == 0
      temp /= 10
      num_zeroes += 1
    end
  end
  num_zeroes
end

# Zeroes are only added when five multiplies [2,4,6,8]
# and zeroes are added for every power of 5 that multiplies
# these numbers.
def z(n)
  power = 5
  num_zeroes = 0
  while power <= n
    num_zeroes += n/power
    power *= 5
  end
  num_zeroes
end

# Run all test cases
if __FILE__ == $0
  while tests = gets
    tests = tests.to_i # around 100_000

    tests.times do |i|
      n = gets.to_i # <= 1_000_000_000
      puts z n
    end

  end
end