Problem Statement

An International Securities Identification Number (ISIN) is a unique international identifier for a financial security such as a stock or bond.

Write a function or program that takes a string as input, and checks whether it is a valid ISIN. It is only valid if it has the correct format,   and   the embedded checksum is correct. Demonstrate that your code passes the test-cases listed below.

The format of an ISIN is as follows:

For this task, you may assume that any 2-character alphabetic sequence is a valid country code. The checksum can be validated as follows:

(The comments are just informational.   Your function should simply return a Boolean result.   See #Raku for a reference solution.)

Related task:

Let's start with the solution:

CHARS = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ'

int checksum(String prefix) {
    def digits = prefix.toUpperCase().collect { CHARS.indexOf(it).toString() }.sum()
    def groups = digits.collect { CHARS.indexOf(it) }.inject([[], []]) { acc, i -> [acc[1], acc[0] + i] }
    def ds = groups[1].collect { (2 * it).toString() }.sum().collect { CHARS.indexOf(it) } + groups[0]
    (10 - ds.sum() % 10) % 10
}

assert checksum('AU0000VXGZA') == 3
assert checksum('GB000263494') == 6
assert checksum('US037833100') == 5
assert checksum('US037833107') == 0