20211202

今天看到有人说20211202这一天很特殊，想起刚学编程那会求某一范围内的回文数。今天闲来无事，计算了一下本世纪的回文日期，发现只有十一个，差不多十年一遇，今天已经是第四个了。希望看到本文的人都能活到2099。^_^

#include <iostream>
#include<iomanip>
using namespace std;

int GetDays(int year, int month)
{
    int days = -1;
    switch (month)
    {
    case 1:
    case 3:
    case 5:
    case 7:
    case 8:
    case 10:
    case 12:
    {
        days = 31;
    }
    break;
    case 4:
    case 6:
    case 9:
    case 11:
    {
        days = 30;
    }
    break;
    case 2:
    {
        days = 28 + (((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0)) ? 1 : 0;
    }
    break;
    default:
        days = -1;
        break;
    }

    return days;
}

bool IsPalindromeDay(int year, int month, int day)
{
    int n1 = day % 10;
    int n2 = day / 10;

    int n3 = month % 10;
    int n4 = month / 10;

    int n5 = year % 10;
    int n6 = (year / 10) % 10;
    int n7 = (year / 100) % 10;
    int n8 = (year / 1000) % 10;

    int arr[] = {n8, n7, n6, n5, n4, n3, n2, n1};

    int count = sizeof(arr) / sizeof(arr[0]);

    int i = 0;
    while ((arr[i] == 0) && (i < (count - 5)))
    {
        ++i;
    }

    int j = count - 1;
    
    while (j > i)
    {
        if (arr[i++] != arr[j--])
        {
            return false;
        }
    }

    return true;
}

int main()
{
    int c = 0;
    for (int year = 2000; year <= 2099; ++year)
    {
        for (int month = 1; month <= 12; ++month)
        {
            int days = GetDays(year, month);
            for (int day = 1; day <= days; ++day)
            {
                if (IsPalindromeDay(year, month, day))
                {
                    cout << setw(4) << setfill(' ') << ++c << " : " << year << "-" << setw(2) << setfill('0') << month << "-" << setw(2) << setfill('0') << day << endl;
                }
            }
        }
    }

    return 0;
}