题解 | 回文日期

#include <stdio.h>

int isLeapYear(int year) {
    if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) {
        return 1;
    }
    return 0;
}

int main() {
    int months[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
    int leapMonths[] = {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
    int beginDate, endDate;
    scanf("%d %d", &beginDate, &endDate);
    int beginYear = beginDate / 10000;
    int endYear = endDate / 10000;
    int count = 0;
    for (int year = beginYear; year <= endYear; ++year) {
        int leap = isLeapYear(year);
        for (int month = 1; month <= 12; ++ month) {
            int monthDays = leap ? leapMonths[month - 1] : months[month - 1];
            for (int day = 1; day <= monthDays; ++day) {
                int date = year * 10000 + month * 100 + day;
                if (beginDate <= date && date <= endDate) {
                    int reverseMonth = (month % 10) * 10 + (month / 10);
                    int reverseDay = (day % 10) * 10 + (day / 10);
                    if (year == reverseDay * 100 + reverseMonth) {
                        ++count;
                    }
                }
            }
        }
    }
    printf("%d\n", count);
    return 0;
}