ruby - Ruby 中的 Luhn 算法

Question

我一直在尝试在 Ruby 中实现 Luhn 算法，但不断收到错误消息，指出无法将 nil 合并到 Fixnum 中。

Luhn 算法应该:

从倒数第二个数字开始，每隔一个数字加倍，直到达到第一个数字

将所有未碰过的数字和翻倍的数字相加(翻倍的数字需要拆开，10变成1+0)

如果总数是 10 的倍数，则您收到了有效的信用卡号!

这是我的:

class CreditCard
  def initialize (card_number)
    if (card_number.to_s.length != 16 )
        raise ArgumentError.new("Please enter a card number with exactly 16 integars")
    end
    @card_number = card_number
    @total_sum = 0
  end

  def check_card
    @new_Array = []
    @new_Array = @card_number.to_s.split('')
    @new_Array.map! { |x| x.to_i }
    @new_Array.each_with_index.map { |x,y| 
      if (y % 2 != 0) 
        x = x*2
      end  
     }  
    @new_Array.map! {|x| 
     if (x > 9)
        x = x-9 
      end  
    }
    @new_Array.each { |x| 
        @total_sum = @total_sum + x
    }  
    if (@total_sum % 10 == 0)
      return true
    else
      return false      
    end  
  end  
end

Answer 1

在你的部分

@new_Array.each_with_index.map { |x,y| 
  if (y % 2 != 0) 
    x = x*2
  end  
}

更改不是永久性的。此外，正如 Victor 所写，如果测试失败，你的@new_Array 将被填充为 nils。最后

if (@total_sum % 10 == 0)
  return true
else
  return false      
end

你可以直接写

@total_sum % 10 == 0

因为 ruby​​ 方法的最后一行已经是一个返回。我找到了一个 slightly different algorithm 并在这里实现了它:

# 1) Reverse the order of the digits in the number.
# 2) Take the first, third, ... and every other odd digit in the reversed digits
#   and sum them to form the partial sum s1
# 3) Taking the second, fourth ... and every other even digit in the reversed digits:
#   a) Multiply each digit by two (and sum the digits if the answer is greater than nine) to form partial sums for the even digits
#   b) Sum the partial sums of the even digits to form s2
# 4) If s1 + s2 ends in zero then the original number is in the form of a valid credit card number as verified by the Luhn test.

def luhn n
  s = n.to_s.reverse
  sum=0
  tmp=0
  (0..s.size-1).step(2) {|k|    #k is odd, k+1 is even
    sum+=s[k].to_i   #s1
    tmp = s[k+1].to_i*2
    tmp = tmp.to_s.split(//).map(&:to_i).reduce(:+) if tmp>9
    sum+=tmp
  }
  sum%10 == 0
end

[49927398716, 49927398717, 1234567812345678, 1234567812345670].each {|num|
  puts "%20s %s" % [num, luhn(num)]
}

#         49927398716 true
#         49927398717 false
#    1234567812345678 false
#    1234567812345670 true

希望这对您有所帮助。