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

IPv4addresses 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.

IPv6addresses 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.

Solution: 分类讨论。注意string.split("x")，如果最后一个字母是x，则后面没有空串

    public String validIPAddress(String IP) {
        if (IP == null || IP.length() == 0) {
            return "Neither";
        }
        String[] parts_4 = IP.split("\\.");
        String[] parts_6 = IP.split(":");
        //注意要有第一个条件。eg: 192.168.1.1.
        if (IP.charAt(IP.length() - 1) != '.' && parts_4.length == 4 && parts_6.length == 1) {
            for (String part : parts_4) {
                if (part.length() > 3 || part.length() == 0 || part.length() > 1 && part.charAt(0) == '0') {
                    return "Neither";
                }
                int val = 0;
                for (int i = 0; i < part.length(); i++) {
                    char c = part.charAt(i);
                    if (c < '0' || c > '9') {
                        return "Neither";
                    }
                    val = val * 10 + c - '0';

                }
                if (val > 255) {
                    return "Neither";
                }
            }
            return "IPv4";
        }
        //注意要有第一个条件
        if (IP.charAt(IP.length() - 1) != ':' && parts_6.length == 8 && parts_4.length == 1) {
            for (String part : parts_6) {
                if (part.length() > 4 || part.length() == 0) {
                    return "Neither";
                }
                for (int i = 0; i < part.length(); i++) {
                    char c = part.charAt(i);
                    if (!(c >= '0' && c <= '9' || c >= 'a' && c <= 'f' || c >= 'A' && c <= 'F')) {
                        return "Neither";
                    }
                }    
            }
            return "IPv6";

        }
        return "Neither";
    }