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 address 172.16.254.01 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: "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.

要考虑的情况：

在判断是查ipv4还是ipv6之前，先找"." 和":", 然后调用split,注意在用split的时候"."在正则表达里是可以匹配任何，所以要用"\\."。

ipv4：不合法情况：

1. 如果string[] 长度不为4

2. string 数组里的每一个数组，不能为空，长度不能为0，

3. 如果string长度为1， 那么其值可以为0，如果不为1，开头不能为0

4. string长度大于4

5. string里有字母

6. parsint以后，大小不在0-255之间

ipv6 不合法情况

1.数组长度不为8； 2. 数组长度大于4； 3。 数组为空或者长度为0； 4。 string每个char的值不在0-9 a-f A-F 之内

class Solution {
    public String validIPAddress(String IP) {
        
        if(IP == null || IP.length() == 0)
            return "Neither";
        
        if(IP.charAt(0) == '.' ||IP.charAt(0) == ':' || IP.charAt(IP.length()-1) == '.' ||IP.charAt(IP.length()-1) == ':')
            return "Neither";
        
        if(IP.indexOf(".") != -1){
            String[] sArray =  IP.split("\\.");
            System.out.println("sArray "+IP.indexOf("."));
            return checkIPv4(sArray);
            
        }
        else if(IP.indexOf(":") != -1){
            String[] sArray =  IP.split(":");
            return checkIPv6(sArray);
        }else{
            return "Neither";
        }
    }
    
    public String checkIPv4(String[] ip){
        
        if(ip.length != 4)
            return "Neither";
        
        
        for(int i =0; i < ip.length; i++){
            String subIp = ip[i];
            System.out.println(subIp);
            //开头不能为0；
            if( subIp == null || subIp.length() == 0 ||(subIp.charAt(0) =='0' && subIp.length() > 1))
                return "Neither";
            
            if(subIp.length() > 4)
                return "Neither";
            
            
            for(int j = 0; j < subIp.length();j++){
                if(subIp.charAt(j) >='0' && subIp.charAt(j) <='9')
                    continue;
                else
                    return "Neither";
            }
            
            
            int nums = Integer.parseInt(subIp);
            
            if(nums< 0 || nums > 255)
                return "Neither";
            
        }
        
        return "IPv4";
        
    }
    
    public String checkIPv6(String[] ip){
        System.out.println("啊啊啊 "+ip.length);
        if(ip.length != 8)
            return "Neither";
        
        for(int i =0; i < ip.length;i++){
            String subIP = ip[i];
            if(subIP == null || subIP.length() == 0 || subIP.length() > 4)
                return "Neither";
            
            for(int j = 0; j < subIP.length() ;j++){
                if((subIP.charAt(j)>= '0' && subIP.charAt(j) <= '9' ) || (subIP.charAt(j)>= 'a' && subIP.charAt(j) <= 'f') || (subIP.charAt(j)>= 'A' && subIP.charAt(j) <= 'F')){
                    continue;
                }
                
                else{
                    return "Neither";
                }
            }
            
            
        }
        
        return  "IPv6";
        
        
    }
}