题解 | #合法IP#

import java.util.*;

import java.io.*;
public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] arr = br.readLine().split("\\.");
        if (arr.length != 4) {
            System.out.print("NO");
            return;
        }
        for (String part : arr) {
            //为空非法
            if("".equals(part)){
                System.out.print("NO");
                return;
            }
            //0开头非法
            if(part.startsWith("0")&&part.length()>1){
                System.out.print("NO");
                return;
            }
            //+-开头非法
            if(part.startsWith("-")||part.startsWith("+")){
                System.out.print("NO");
                return;
            }
            int cur = 0;
            try {
                cur = Integer.valueOf(part);
            } catch (Exception e) {
                //非数字非法
                System.out.print("NO");
                return;
            }
            //不在0-255之间非法
            if (cur < 0 || cur > 255) {
                System.out.print("NO");
                return;
            }
        }
        System.out.print("YES");
    }
}