468. Validate IP Address

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.,172.16.254.1;

Besides, leading zeros in the IPv4 is invalid. For example, the address172.16.254.01is 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 address2001:0db8:85a3:0000:0000:8a2e:0370:7334is 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, so2001:db8:85a3:0:0:8A2E:0370:7334is 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:0370:7334is an invalid IPv6 address.

Besides, extra leading zeros in the IPv6 is also invalid. For example, the address02001:0db8:85a3:0000:0000:8a2e:0370:7334is invalid.

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

Example 1:

Input: "172.16.254.1"


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: "256.256.256.256"


Output: "Neither"


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

Code: Java Regex

public class Solution {
    public String validIPAddress(String IP) {
        if(IP.matches("(([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])\\.){3}([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])"))return "IPv4";
        if(IP.matches("(([0-9a-fA-F]{1,4}):){7}([0-9a-fA-F]{1,4})"))return "IPv6";
        return "Neither";
    }
}

Python: using int

class Solution(object):
    def validIPAddress(self, IP):

        def isIPv4(s):
            try: return str(int(s)) == s and 0 <= int(s) <= 255 #  str(int(s)) == s enforces to drop the leading 0's and all numbers a non-characters
            except: return False

        def isIPv6(s):
            if len(s) > 4 : return False # only allows less that 4
            try: return int(s, 16) >= 0 and s[0] != '-' and s[0] != '+' # to prevent int to conver +xxx or -xxx
            except: return False

        if IP.count(".") == 3 and all(isIPv4(i) for i in IP.split(".")): 
            return "IPv4"
        if IP.count(":") == 7 and all(isIPv6(i) for i in IP.split(":")): 
            return "IPv6"
        return "Neither"

C++ Normal

class Solution {
public:
 const string validIPv6Chars = "0123456789abcdefABCDEF";
 const string digits = "0123456789";
    bool isValidIPv4Block(string& block) {
        int num = 0;
        //check length
        if (block.size() > 0 && block.size() <= 3) {
            for (int i = 0; i < block.size(); i++) {
                char c = block[i];
                // check value
                if (digits.find(c)== string::npos || (i == 0 && c == '0' && block.size() > 1))  // special case: if c is a leading zero
                return false;
                else {
                num *= 10;
                num += c - '0';
                }
            }
            return num <= 255;
        }
        return false;
    }

    bool isValidIPv6Block(string& block) {
        //check length
        if (block.size() > 0 && block.size() <= 4) {
            for (int i = 0; i < block.size(); i++) {
                char c = block[i];
                 // check value
                if (validIPv6Chars.find(c) == string::npos)
                    return false;
            }
            return true;
        }
        return false;
    }

    string validIPAddress(string IP) {
        stringstream ss(IP);
        string block;
        // ipv4 candidate
        if (IP.substr(0, 4).find('.') != string::npos) {
            for (int i = 0; i < 4; i++) {
            if (!getline(ss, block, '.') || !isValidIPv4Block(block))
                   return "Neither";
            }
            return ss.eof() ? "IPv4" : "Neither";
        }
        // ipv6 candidate
        else if (IP.substr(0, 5).find(':') != string::npos) {
            for (int i = 0; i < 8; i++) {
            if (!getline(ss, block, ':') || !isValidIPv6Block(block))
                return "Neither";
            }
            return ss.eof() ? "IPv6" : "Neither";
        }

        return "Neither";
    }
};