题解 | #验证IP地址#

import java.util.*;


public class Solution {
    /**
     * 验证IP地址
     * @param IP string字符串 一个IP地址字符串
     * @return string字符串
     */
    public String solve (String IP) {
        boolean is = false;
        if (isIPv4(IP)) {
            return "IPv4";
        } else if (isIPv6(IP)) {
            return "IPv6";
        } else {
           return "Neither";
        }

    }

    private boolean isIPv4(String ip){
        if(ip==null || ip.isEmpty()) return false;
        String[] split = ip.split("\\.", -1);
        if(split.length!=4) return false;
        for (String s : split) {
            if (s.isEmpty() || s.length() > 3) return false;
            if (s.equals("0")) continue;
            if (s.startsWith("0")) return false;
            for (int j = 0; j < s.length(); j++) {
                char c = s.charAt(j);
                if (c < '0' || c > '9') return false;
            }
            if(s.compareTo("255")>0) return false;
        }
        return true;
    }

    private boolean isIPv6(String ip){
        if(ip==null || ip.isEmpty()) return false;
        String[] split = ip.split(":", -1);
        if(split.length!=8) return false;
        for (String s : split) {
            if (s.isEmpty() || s.length() > 4) return false;
            if (s.equals("00") || s.equals("000") || s.equals("0000")) return false;
            for (int j = 0; j < s.length(); j++) {
                char c = s.charAt(j);
                if (!(c >= '0' && c <= '9') && !(c >= 'a' && c <= 'f') && !(c >= 'A' && c <= 'F')) return false;
            }
        }
        return true;
    }
}