Project Eueler: problem21

問題

Let d(n) be defined as the sum of proper divisors of n (numbers less than n which divide evenly into n).
If d(a) = b and d(b) = a, where a b, then a and b are an amicable pair and each of a and b are called amicable numbers.

For example, the proper divisors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110; therefore d(220) = 284. The proper divisors of 284 are 1, 2, 4, 71 and 142; so d(284) = 220.

Evaluate the sum of all the amicable numbers under 10000.

回答

def calc_dev(n)
  y = [1]
  i = 2
  while i <= n/2
    y << i if n % i == 0
    i += 1
  end
  return y
end

def chk_ami(n)
  sum1 = calc_dev(n).inject(0){|sum,x| sum + x}
  sum2 = calc_dev(sum1).inject(0){|sum,x| sum + x}
  if n == sum2 && n != sum1
    return true
  else
    return false
  end
end

def find_total_ami(n)
  total = 0
  1.upto(n).each do |v|
    total += v if chk_ami(v)
  end
  return total
end

p find_total_ami(10000)

備考

遅い。
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