题解 | #合法IP#

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String[] s = in.nextLine().split("\\.");
        if(s.length == 4){
            for(int i=0; i<4; i++){
                String ss = s[i];
                if(ss.isEmpty()){
                    System.out.print("NO");
                    return;
                }
                for(int j=0; j<ss.length(); j++){
                    char c = ss.charAt(j);
                    if(!Character.isDigit(c)){
                        System.out.print("NO");
                        return;
                    }
                }   
                if(Integer.parseInt(ss) < 0 || Integer.parseInt(ss) > 255){
                    System.out.print("NO");
                    return;
                }
                if(String.valueOf(Integer.parseInt(ss)).length() != ss.length()){
                    System.out.print("NO");
                    return;
                }
            }
            System.out.print("YES");
        }else{
            System.out.print("NO");
        }
    }
}