POJ 1446 - Moscow Time - 模拟

题目大意：

输入年、月、日、星期、小时、分钟、秒，以及所处的时区，要求将其转换成UTC+3时区内的时间。

浑身都是坑的模拟题。

①题目没有说是单组还是多组数据（其他OJ上的版本是多组数据），保险起见建议处理到EOF。

②"Year: Set by two or four decimal digits. If a year is set by two decimals it is assumed that this is a number of the year of the XX century."

我查了谷歌翻译才反应过来那个XX是罗马数字20……输入年份时不能直接"%d"，得先读成字符串，再判断长度，如果长度为2则在转成整数时需要加上1900。

③"First two digits set the hours and the last two the minutes of offset value."

在求该时区与UTC+3相差的偏移量时，不能简单粗暴地用300减去读入的数。假如输入+0130，那么300－130的结果就是170，该结果显然是错误的。

④"The absolute value of the difference does not exceed 24 hours."

注意-2350这样的极端情形，加的天数有可能是2天！（虽然现实中不存在-2350这样的时区划分，但本题的数据就不好说了）

⑤"Your program should rely on the predefined correctness of the given Day-of-week and Time-zone."

这句话的意思其实是说输入数据保证格式和内容都是正确的，我一开始看到这句还愣了一会儿（没见过这种操作）……

⑥"February, as a rule, has 28 days, save for the case of the leap year (29 days)."

学到了一个新短语：save for（手动笑哭

本题是需要考虑闰年的，闰年的判定法与现实一致：四年一闰，百年不闰，四百年再闰。

⑦"The output string should not include leading and trailing spaces."

注意行末不能有空格。另外输出时一定要注意加前导零。

AC代码：

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <stdexcept>
#include <string>

const char dayOfWeekName[7][4] = {
        "SUN",
        "MON",
        "TUE",
        "WED",
        "THU",
        "FRI",
        "SAT"
};
const char monthName[12][4] = {
        "JAN",
        "FEB",
        "MAR",
        "APR",
        "MAY",
        "JUN",
        "JUL",
        "AUG",
        "SEP",
        "OCT",
        "NOV",
        "DEC"
};
const char timeZoneOffsetName[6][4] = {
        "UT",
        "GMT",
        "EDT",
        "CDT",
        "MDT",
        "PDT"
};
const int timeZoneOffset[6] = {0, 0, -400, -500, -600, -700};
const int dayNumberOfMonth[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; //non-leap year

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

inline int getMonthId(const char* month)
{
    for (int i = 0; i < 12; i++)
        if (strcmp(month, monthName[i]) == 0)
            return i;

    throw std::invalid_argument("invalid month name: " + std::string(month));
}

inline int getDayOfWeekId(const char* dayOfWeek)
{
    for (int i = 0; i < 7; i++)
        if (strcmp(dayOfWeek, dayOfWeekName[i]) == 0)
            return i;

    throw std::invalid_argument("invalid day of week: " + std::string(dayOfWeek));
}

int getOffset(const char* timeZone)
{
    if (timeZone[0] == '+' || timeZone[0] == '-') //in digit form
        //return 300 - atoi(timeZone); //WRONG!!!
    {
        int tz = atoi(timeZone); //example: +0235
        if (tz > 0 && tz < 300)
            tz += 40; //+0235 -> 275
        return 300 - tz; //+0235 -> 275 -> +0025
    }
    else
        for (int i = 0; i < 6; i++)
            if (strcmp(timeZone, timeZoneOffsetName[i]) == 0)
                return 300 - timeZoneOffset[i];

    throw std::invalid_argument("invalid time zone: " + std::string(timeZone));
}

int advanceClock(int& hour, int& minute, int offset)
{
    if (offset >= 0)
    {
        minute += offset % 100;
        if (minute >= 60)
        {
            minute -= 60;
            hour += 1;
        }
        hour += offset / 100;
        if (hour >= 24)
        {
            int temp = hour / 24;
            hour %= 24;
            return temp;
        }
    }
    else //offset < 0
    {
        minute -= (-offset % 100);
        if (minute < 0)
        {
            minute += 60;
            hour -= 1;
        }
        hour -= (-offset / 100);
        if (hour < 0)
        {
            hour += 24;
            return -1;
        }
    }
    return 0;
}

void forwardDate(int& year, char* month, int& dayOfMonth, char* dayOfWeek, int offset)
{
    int monthId = getMonthId(month); //0-based
    int curDayNumber = dayNumberOfMonth[monthId] + (monthId == 1 && isLeapYear(year));

    int dayOfWeekId = getDayOfWeekId(dayOfWeek);
    strcpy(dayOfWeek, dayOfWeekName[(dayOfWeekId + 1) % 7]);

    if ((dayOfMonth += offset) > curDayNumber)
    {
        dayOfMonth = 1;
        if ((monthId += 1) >= 12)
        {
            monthId = 0;
            year += 1;
        }
    }
    strcpy(month, monthName[monthId]); //maybe advanced before
}

void backwardDate(int& year, char* month, int& dayOfMonth, char* dayOfWeek)
{
    int monthId = getMonthId(month); //0-based

    int dayOfWeekId = getDayOfWeekId(dayOfWeek);
    strcpy(dayOfWeek, dayOfWeekName[(dayOfWeekId + 6) % 7]);

    if ((dayOfMonth -= 1) <= 0)
    {
        if ((monthId -= 1) < 0)
        {
            monthId = 11;
            year -= 1;
        }
        dayOfMonth = dayNumberOfMonth[monthId] + (monthId == 1 && isLeapYear(year));
        //update dayOfMonth before monthId
    }
    strcpy(month, monthName[monthId]);
}

bool solve()
{
    char dayOfWeek[5];
    char month[4];
    char timeZone[8];
    char yearStr[5];
    int dayOfMonth;
    int year;
    int hour, minute, second;
    int offset;

    if (scanf("%s%d%s%s%d:%d:%d%s", dayOfWeek, &dayOfMonth, month, yearStr,
              &hour, &minute, &second, timeZone) == EOF)
        return false;

    dayOfWeek[3] = '\0'; //erase the comma
    year = (strlen(yearStr) == 4 ? atoi(yearStr) : 1900 + atoi(yearStr));

    offset = getOffset(timeZone);
    int advanceClockResult = advanceClock(hour, minute, offset);

    if (advanceClockResult >= 1)
        forwardDate(year, month, dayOfMonth, dayOfWeek, advanceClockResult);
    else if (advanceClockResult == -1)
        backwardDate(year, month, dayOfMonth, dayOfWeek);

    printf("%s, %02d %s %04d %02d:%02d:%02d +0300",
           dayOfWeek, dayOfMonth, month, year, hour, minute, second);

    return true;
}

int main()
{
    for (int i = 0; solve(); i++)
    {
        if (i > 0)
            putchar('\n');
    }
    return 0;
}