题解 | 回文日期 c#

using System;
using System.Collections.Generic;
using System.Linq;
public class Program {
    public static bool IsPalindrome(string s) {
        return s.SequenceEqual(s.Reverse());
    }
    public static void Main() {
        //这题c#暴力枚举超时了
        /*
        string start = Console.ReadLine();
        string end = Console.ReadLine();
        string format = "yyyyMMdd";

        //将获得的日期字符串转换为DateTime类型
        var startDate = DateTime.ParseExact(start, format, null);
        var endDate = DateTime.ParseExact(end, format, null);

        int count = 0;
        //用AddDays方法获取下一天的DateTime实例，再转换为String判断是否回文
        for (var date = startDate; date <= endDate; date = date.AddDays(1)) {
            var dateString = date.ToString(format);
            if (IsPalindrome(dateString)) {
                count++;
                //Console.WriteLine($"{dateString} 是回文日期！");
            }
        }

        Console.WriteLine(count); */

        //所以应该对每个年份 y，生成回文日期字符串然后判断是否合法

        string start = Console.ReadLine(); // e.g., "20110101"
        string end = Console.ReadLine();   // e.g., "20111231"
        string format = "yyyyMMdd";

        int startYear = int.Parse(start.Substring(0, 4));
        int endYear = int.Parse(end.Substring(0, 4));

        int count = 0;

        // 遍历年份
        for (int year = startYear; year <= endYear; year++) {
            // 生成回文日期字符串
            string yearStr = year.ToString("D4");
            string reversedYear = new string(yearStr.Reverse().ToArray());
            string palindromeDateStr = yearStr + reversedYear; // yyyymmdd

            // 跳过范围外的日期
            if (string.Compare(palindromeDateStr, start) < 0) 
            continue;
            if (string.Compare(palindromeDateStr, end) > 0) 
            break;

            // 检查是否是合法日期
            if (DateTime.TryParseExact(palindromeDateStr, format, null,System.Globalization.DateTimeStyles.None, out _)) {
                count++;
            }
        }

        Console.WriteLine(count);
    }
}