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) {
        // write code here
        if(isIpv4(IP)){
            return "IPv4";
        }else if(isIpv6(IP)){
            return "IPv6";
        }else{
            return "Neither";
        }
        
    }
    public boolean isIpv4(String IP){
        if(IP.indexOf(".") == -1){
            return false;
        }
        
        String[] ips = IP.split("\\.");
        if(ips.length != 4){
            return false;
        }
        for(int i = 0;i<ips.length;i++){
            if(ips[i].length() == 0){
                return false;
            }
            if(ips[i].length()>3 || (ips[i].charAt(0)=='0' && ips[i].length() != 1)){
                return false;
            }
            for(int j = 0;j<ips[i].length();j++){
                if(ips[i].charAt(j) < '0' || ips[i].charAt(j)>'9'){
                    return false;
                }
            }
            int num = Integer.parseInt(ips[i]);
            if(num<0 || num>255){
                return false;
            }
        }
        return true;
    }
    public boolean isIpv6(String IP){
        if(IP.indexOf(":") == -1){
            return false;
        }
        
        String[] ips = IP.split(":",-1);
        if(ips.length != 8){
            return false;
        }
        
        for(int i=0;i<ips.length;i++){
            if(ips[i].length() == 0){
                return false;
            }
            
            if(ips[i].length() > 4){
                return false;
            }
            
            for(int j = 0;j<ips[i].length();j++){
                char c = ips[i].charAt(j);
                boolean flag = (c>='0'&&c<='9') || (c>='a' && c<='f') || (c>='A' && c<='F');
                if(!flag){
                    return false;
                }
            }
        }
        return true;
        
    }
}