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 scanner = new Scanner(System.in);
        scanner.useDelimiter("\n");
        String result = "YES";
        while (scanner.hasNext()) {
            String S = scanner.next();
            String[] s = S.split("\\.");
            if (s.length != 4) {
                result = "NO";
                System.out.println(result);
                continue;
            }
            for (int i = 0; i < s.length; i++) {
                if (!is(s[i], i)) {
                    result = "NO";
                    break;
                }
            }
            System.out.println(result);
        }
    }

    public static boolean is(String value, int index) {
        if (value == null || value.equals("")) return false;
        int sum = 0;
        for (int i = 0; i < value.length(); i++) {
            char c = value.charAt(i);
            if (!Character.isDigit(c) || (i == 0 && Character.isDigit(c) && c == '0'  && value.length()>1)) {
                return false;
            } else {
                sum = sum * 10 + c-'0';
            }
        }
        return sum < 255 && sum >= 0;
    }
}