题解 | 回文日期

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 平年每月的天数
        int[] commonYear = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
        // 闰年每月的天数
        int[] leapYear = {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
        
        String startDate = in.nextLine();
        String endDate = in.nextLine();
        int count = 0;

        // 解析起始日期
        int startYear = Integer.parseInt(startDate.substring(0, 4));
        int startMonth = Integer.parseInt(startDate.substring(4, 6));
        int startDay = Integer.parseInt(startDate.substring(6));
        
        // 解析结束日期
        int endYear = Integer.parseInt(endDate.substring(0, 4));
        int endMonth = Integer.parseInt(endDate.substring(4, 6));
        int endDay = Integer.parseInt(endDate.substring(6));

        // 遍历所有可能的年份
        for (int year = startYear; year <= endYear; year++) {
            // 从年份生成回文的月份和日期
            String yearStr = String.valueOf(year);
            int month = Integer.parseInt("" + yearStr.charAt(3) + yearStr.charAt(2));
            int day = Integer.parseInt("" + yearStr.charAt(1) + yearStr.charAt(0));
            
            // 判断是否为闰年
            boolean isLeap = false;
            if ((year % 400 == 0) || (year % 4 == 0 && year % 100 != 0)) {
                isLeap = true;
            }
            
            // 获取该年份每月的天数
            int[] monthDays = isLeap ? leapYear : commonYear;
            
            // 检查月份和日期是否合法
            if (month < 1 || month > 12 || day < 1 || day > monthDays[month - 1]) {
                continue;
            }
            
            // 将回文日期转换为整数形式
            int palindromeDate = year * 10000 + month * 100 + day;
            int startDateInt = Integer.parseInt(startDate);
            int endDateInt = Integer.parseInt(endDate);
            
            // 检查日期是否在范围内
            if (palindromeDate >= startDateInt && palindromeDate <= endDateInt) {
                count++;
            }
        }

        System.out.println(count);
    }
}