题解 | #验证IP地址#

import java.util.*;

/**
 * NC113 验证IP地址
 * @author d3y1
 */
public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 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) {
        // return solution1(IP);
        return solution2(IP);
    }

    /**
     * 分段法
     * @param IP
     * @return
     */
    private String solution1(String IP){
        if(IP.contains(".")){
            if(isIPv4(IP)){
                return "IPv4";
            }
        }
        if(IP.contains(":")){
            if(isIPv6(IP)){
                return "IPv6";
            }
        }

        return "Neither";
    }

    /**
     * 是否IPv4
     * @param IP
     * @return
     */
    private boolean isIPv4(String IP){
        String[] parts = IP.split("\\.", -1);
        if(parts.length != 4){
            return false;
        }
        // String regex = "\\d{1,3}";
        String regex = "[0-9]{1,3}";
        for(String part: parts){
            if(!part.matches(regex)){
                return false;
            }
            if(part.length()>1 && part.startsWith("0")){
                return false;
            }
            if(255 < Integer.parseInt(part)){
                return false;
            }
        }

        return true;
    }

    /**
     * 是否IPv6
     * @param IP
     * @return
     */
    private boolean isIPv6(String IP){
        String[] parts = IP.split(":", -1);
        if(parts.length != 8){
            return false;
        }
        String regex = "[0-9a-fA-F]{1,4}";
        for(String part: parts){
            if(!part.matches(regex)){
                return false;
            }
        }

        return true;
    }

    /**
     * 正则表达式
     * @param IP
     * @return
     */
    private String solution2(String IP){
        String regexIPv4 = "(([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])";
        String regexIPv6 = "(([0-9a-fA-F]{1,4}):){7}([0-9a-fA-F]{1,4})";

        if(IP.matches(regexIPv4)){
            return "IPv4";
        }
        if(IP.matches(regexIPv6)){
            return "IPv6";
        }

        return "Neither";
    }
}