IP Validation Algorithm in Ruby

Today we're gonna take a stab at a Medium LeetCode problem. For a long time I never even attempted these because I was worried that they'd be "too hard", but this example will demonstrate that this is not the case.

Join me as we dive into the problem, the solution written out in English, then break down my algorithm to solve this algorithm. We will learn a little bit about IP addresses, and Ruby's nifty string manipulation methods.

Let's dive in!

The Problem

Given a string queryIP, return "IPv4" if IP is a valid IPv4 address, "IPv6" if IP is a valid IPv6 address or "Neither" if IP is not a correct IP of any type.

A valid IPv4 address is an IP in the form "x[1].x[2].x[3].x[4]" where 0 <= x[i] <= 255 and x[i] cannot contain leading zeros. For example, "192.168.1.1" and "192.168.1.0" are valid IPv4 addresses while "192.168.01.1", "192.168.1.00", and "192.168@1.1" are invalid IPv4 addresses.

A valid IPv6 address is an IP in the form "x[1]:x[2]:x[3]:x[4]:x[5]:x[6]:x[7]:x[8]" where: 1 <= x[i].length <= 4

x[i] is a hexadecimal string that may contain digits, lowercase English letters ('a' to 'f') and upper-case English letters ('A' to 'F'). Leading zeros are allowed in x[i]. For example, "2001:0db8:85a3:0000:0000:8a2e:0370:7334" and "2001:db8:85a3:0:0:8A2E:0370:7334" are valid IPv6 addresses, while "2001:0db8:85a3::8A2E:037j:7334" and "02001:0db8:85a3:0000:0000:8a2e:0370:7334" are invalid IPv6 addresses.

Understanding IP Addresses

An Internet Protocol address (IP address) is a unique identifier for devices on a network. There are two types of IP addresses in common use:

1. IPv4: The IPv4 (Internet Protocol version 4) is a numerical label assigned to each device in a computer network that uses the Internet Protocol. An IPv4 address consists of four numbers separated by periods. Each number can be between 0 and 255.

2. IPv6: The IPv6 (Internet Protocol version 6) is the most recent version of the Internet Protocol. An IPv6 address consists of eight groups of one to four hexadecimal digits, separated by colons. Each hexadecimal digit is a number from 0-9 or a letter from A-F.

Solution in English

In our solution, we distinguish between IPv4 and IPv6 addresses by their delimiters: periods for IPv4, and colons for IPv6. We split the input string accordingly.

For each segment resulting from the split, we validate its contents and length based on the respective IPv4 and IPv6 standards.

For IPv6 addresses, we additionally check that each segment only contains valid hexadecimal characters.

If the input string matches the criteria for either IPv4 or IPv6, we return the corresponding string. If it matches neither, we return "Neither".

This approach efficiently checks the validity of the IP address by inspecting each segment individually and verifying its conformance to the standards of either IP version.

Worth noting: you can totally use RegEx to solve this problem. I'm not going to, for clarity.

Code Solution

def valid_ip_address(query_ip)
    ipv4 = query_ip.split('.')
    ipv6 = query_ip.split(':')

    return "IPv4" if ipv4.length == 4 && is_ipv4(ipv4)
    return "IPv6" if ipv6.length == 8 && is_ipv6(ipv6)

    "Neither"
end

def is_ipv4(ipv4)
    ipv4.all? do |part|
        part == part.to_i.to_s && part.to_i.between?(0, 255)
    end
end

def is_ipv6(ipv6)
    ipv6.all? do |part|
        part.length.between?(1, 4) && is_hex(part)
    end
end

def is_hex(s)
    s.each_char.all? { |char| '0123456789abcdefABCDEF'.include?(char) }
end

Code Breakdown

First, we split the arrays up. To visualize how this shakes out, I've included a couple smaller diagrams below

IPv4

IPv6

Once we've split up the IP addresses into arrays, we can then iterate through each part and validate that the data aligns with how we expect it to. Diving further into each of the methods below:

• valid_ip_address: This is the main function that splits the IP address by '.' and ':' to separate its components, and check whether it can be a valid IPv4 or IPv6 address based on the length of each part.

• is_ipv4: Checks if all parts of the potential IPv4 address are integers without leading zeroes and are within the range 0-255.

• is_ipv6: Checks if all parts of the potential IPv6 address contain 1 to 4 characters and these characters are hexadecimal digits.

• is_hex: Checks whether every character in the given string is a valid hexadecimal character, which includes the digits 0-9 and the letters a-f or A-F.

Final Thoughts

Usually, Medium LeetCode problems will add one or two extra layers of complexity that make problems more difficult. This does not make them unsolvable!

Break each one down in English first, and take your time. Once you've got it solved in English and you understand the problem, only then write code.

As you solve more and more of these problems, they become less daunting and more like challenges you're prepared to tackle.

Thanks for reading!