0468. Validate IP Address

https://leetcode.com/problems/validate-ip-address

Description

Given a string IP, 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 "x1.x2.x3.x4" where 0 <= xi <= 255 and xi cannot contain leading zeros. For example, "192.168.1.1" and "192.168.1.0" are valid IPv4 addresses but "192.168.01.1", while "192.168.1.00" and "192.168@1.1" are invalid IPv4 addresses.

A valid IPv6 address is an IP in the form "x1:x2:x3:x4:x5:x6:x7:x8" where:

• 1 <= xi.length <= 4

• xi is a hexadecimal string which may contain digits, lower-case English letter ('a' to 'f') and upper-case English letters ('A' to 'F').

• Leading zeros are allowed in xi.

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.

Example 1:

**Input:** IP = "172.16.254.1"
**Output:** "IPv4"
**Explanation:** This is a valid IPv4 address, return "IPv4".

Example 2:

**Input:** IP = "2001:0db8:85a3:0:0:8A2E:0370:7334"
**Output:** "IPv6"
**Explanation:** This is a valid IPv6 address, return "IPv6".

Example 3:

**Input:** IP = "256.256.256.256"
**Output:** "Neither"
**Explanation:** This is neither a IPv4 address nor a IPv6 address.

Example 4:

**Input:** IP = "2001:0db8:85a3:0:0:8A2E:0370:7334:"
**Output:** "Neither"

Example 5:

**Input:** IP = "1e1.4.5.6"
**Output:** "Neither"

Constraints:

• IP consists only of English letters, digits and the characters '.' and ':'.

ac

class Solution {
    public String validIPAddress(String IP) {
        int i4 = IP.indexOf(".");
        int i6 = IP.indexOf(":");
        if (i4 >= 0 && i6 < 0) {
            if (valid4(IP)) return "IPv4";
        } else if (i6 >= 0 && i4 < 0) {
            if (valid6(IP)) return "IPv6";
        }

        return "Neither";
    }

    public boolean valid4(String s) {
        String[] strs = s.split("\\.");
        if (strs.length != 4 || s.charAt(s.length()-1) == '.') return false;
        for (String str : strs) {
            if (str.length() == 0 || 
                str.length() > 1 && str.startsWith("0") || str.length() > 3) return false;
            for (char c : str.toCharArray()) {
                if (!Character.isDigit(c)) return false;
            }
            int val = Integer.parseInt(str);
            if (val < 0 || val > 255) return false;
        }
        return true;
    }

    public boolean valid6(String s) {
        String[] strs = s.split(":");
        if (strs.length != 8 || s.charAt(s.length()-1) == ':') return false;
        for (String str : strs) {
            if (str.length() == 0 || str.length() > 4) return false;
            for (char c : str.toUpperCase().toCharArray()) {
                if ((c < '0' || c > '9') && (c < 'A' || c > 'F')) return false;
            }
        }

        return true;
    }
}

/*
1) v4 only contains ., v6 only contains : 2) split by ./:, careful "\\."; 3) check String[] length, last char can't be seperator; 4) check each char length; 5) check char within range;
*/