C# Program to Validate IP Address

Hi geeks, in this article we going to see about the Leetcode’s Validate Ip Address Problem. This is one of the important interview question.

There are different ways to solve this problem like Naive Approach, Straight Forward Approach, etc. But I solved this problem in a efficient way by using Microsoft framework’s packages like System.Net, System.Net.Sockets and System.Text.RegularExpressions.

Ok, let us jump into the question.

Write a function to check whether an input string is a valid IPv4 address or IPv6 address or neither.

IPv4 addresses are canonically represented in dot-decimal notation, which consists of four decimal numbers, each ranging from 0 to 255, separated by dots (“.”), e.g.,;

Besides, leading zeros in the IPv4 is invalid. For example, the address is invalid.

IPv6 addresses are represented as eight groups of four hexadecimal digits, each group representing 16 bits. The groups are separated by colons (“:”). For example, the address 2001:0db8:85a3:0000:0000:8a2e:0370:7334 is a valid one. Also, we could omit some leading zeros among four hexadecimal digits and some low-case characters in the address to upper-case ones, so 2001:db8:85a3:0:0:8A2E:0370:7334 is also a valid IPv6 address(Omit leading zeros and using upper cases).

However, we don’t replace a consecutive group of zero value with a single empty group using two consecutive colons (::) to pursue simplicity. For example, 2001:0db8:85a3::8A2E:0370:7334 is an invalid IPv6 address.

Besides, extra leading zeros in the IPv6 is also invalid. For example, the address 02001:0db8:85a3:0000:0000:8a2e:0370:7334 is invalid.

Note: You may assume there is no extra space or special characters in the input string.

Example 1:

Input: ""

Output: "IPv4"

Explanation: This is a valid IPv4 address, return "IPv4".

Example 2:

Input: "2001:0db8:85a3:0:0:8A2E:0370:7334"

Output: "IPv6"

Explanation: This is a valid IPv6 address, return "IPv6".

Example 3:

Input: ""

Output: "Neither"

Explanation: This is neither a IPv4 address nor a IPv6 address.


C# Program with detailed explanations:

//To access IPAddress, in-built functionality
using System.Net; 

//To access AddressFamily, so that we can compare our IP Address with Ipv6
//That is, AddressFamily.InterNetworkV6(Ipv6)
using System.Net.Sockets; 

//To access Regex.IsMatch()
using System.Text.RegularExpressions;

public class Solution {
    public string ValidIPAddress(string IP) {
        /*With the help of package System.Net, we are checking the input
        IP string is valid IP Address or not! 
        We are using IPAddress.TryParse(),
        it tries to convert the string into valid IP, 
        when it fails to convert that, it returns "Neither" 
        if(IPAddress.TryParse( IP, out var address) == false)
            return "Neither";
        /*To check our IPAddress is Ipv6 
        When it satifies this condition, we clearly now that, our input
        IP is in the range of IPv6
        if(address.AddressFamily == AddressFamily.InterNetworkV6)
            //Checking this condition
            However, we don't replace a consecutive group of zero value with a single empty group using two consecutive colons (::) to pursue simplicity. For example, 2001:0db8:85a3::8A2E:0370:7334 is an invalid IPv6 address*/
            if(IP.IndexOf("::") > -1)
                return "Neither";
            return "IPv6";
        //Ipv4 condition
            //Ipv4 address should not have leading zero
                return "Neither";
            else if(IP.Count(c => c == '.') != 3)
                return "Neither";
                return "IPv4";
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