1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
|
require "spec_helper"
# The Luhn test is used by some credit card companies to
# distinguish valid credit card numbers from what could
# be a random selection of digits.
#
# For example, if the trial number is 49927398716:
#
# 1. Reverse the digits:
# 61789372994
# 2. Sum the odd digits:
# 6 + 7 + 9 + 7 + 9 + 4 = 42 = s1
# 3. The even digits:
# 1, 8, 3, 2, 9
# 4. Two times each even digit:
# 2, 16, 6, 4, 18
# 5. Sum the digits of each multiplication:
# 2, 7, 6, 4, 9
# 6. Sum the last:
# 2 + 7 + 6 + 4 + 9 = 28 = s2
#
# s1 + s2 = 70 which ends in zero which means {
# that 49927398716 passes the Luhn test
class Luhn
def self.valid?(credit_card)
x = credit_card.digits.each_with_index.inject(Hash.new { |hash, key| hash[key] = [] }) do |memo, (digit, index)|
index.even? ? memo[:odd].push(digit) : memo[:even].push(digit)
memo
end
step_2 = x[:odd].sum
step_3 = x[:even]
step_4 = step_3.map { |x| x * 2 }
step_5 = step_4.map { |x| x.digits.sum }
step_6 = step_5.sum
(step_2 + step_6).digits[0].zero?
end
end
RSpec.describe Luhn do
subject { Luhn }
describe ".valid?" do
specify { expect(subject).to be_valid(49927398716) }
specify { expect(subject).not_to be_valid(49927398717) }
specify { expect(subject).not_to be_valid(1234567812345678) }
specify { expect(subject).to be_valid(1234567812345670) }
end
end
|
