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https://github.com/TheAlgorithms/C
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6072e3b111
* sudoku - lots of documentation and bug fixes Signed-off-by: Krishna Vedala <7001608+kvedala@users.noreply.github.com> * fix uint8_t format specifier * fix format specifiers * fix space in doc * fix doc for get_next_unknown * fix docs and lgtm alert in euler problem 19 * fix docs & lgtm error fibonacci_fast * fix docs & lgtm alert merge_sort * free dynamic memory
136 lines
3.5 KiB
C
136 lines
3.5 KiB
C
/**
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* \file
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* \brief [Problem 19](https://projecteuler.net/problem=19) solution
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* \author [Krishna Vedala](https://github.com/kvedala)
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*/
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#include <stdio.h>
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/**
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* Function to get the number of days in a month.
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* \param month month identified by an integer -\n
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* > 0 = Jan and 11 = December
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* \returns number of days in given month
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* \note For February, adjust for leap year outside the function.
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*/
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char get_month_days(short month)
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{
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if (month == 1) /* February has 28 days. Adjust leap year in the loop */
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return 28;
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else if (month <= 6) /* odd months till July have 30 days - Jan = 0 (even)*/
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{
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if (month & 0x01)
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return 30;
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else
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return 31;
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}
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// else if (month >= 7) /* odd months after July have 31 days*/
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if (month & 0x01)
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return 31;
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return 30;
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}
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/**
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* @brief Check if input year is a leap year.
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* \param year year to check
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* \return 1 if input year is a leap year
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* \return 0 if input year is not a leap year
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*/
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char is_leap_year(short year)
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{
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if ((year % 400 == 0) || ((year % 4 == 0) && (year % 100 != 0)))
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return 1;
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return 0;
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}
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#ifdef DEBUG
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/** Function to convert integer month to string
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* \param day integer identifier of day (0 = Sunday and 7 = Saturday
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* \return pointer to string representation)
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*/
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const char *day_string(int day)
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{
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switch (day)
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{
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case 0:
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return "Sunday";
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case 1:
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return "Monday";
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case 2:
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return "Tuesday";
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case 3:
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return "Wednesday";
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case 4:
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return "Thursday";
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case 5:
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return "Friday";
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case 6:
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return "Saturday";
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default:
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return "Shouldn't see this!";
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}
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}
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#endif
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/** Main function */
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int main(int argc, char **argv)
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{
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int count_sundays = 0;
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const short start_year = 1901;
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const short end_year = 2000;
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/*
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* Let us identify days i.e., Sunday thru Saturday with integers - 0 thru 6
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* respectively Jan 1 1901 was a Tuesday
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*/
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char start_day = 2;
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for (int year = start_year; year <= end_year; year++)
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{
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char is_leap = is_leap_year(year);
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for (char month = 0; month < 12; month++)
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{
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/*
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* These two for-loops count the start of day for the next month.
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* Hence, we have to skip the last December count
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*/
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if (year == end_year && month == 11)
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continue;
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int days = get_month_days(month);
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if (is_leap && month == 1) /* for a leap year february, add a day */
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days++;
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#ifdef DEBUG
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if (year == end_year)
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{
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printf("Year: %d\t Month: %d\t Days: %d\t First of day: %s\n",
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year, month, days, day_string(start_day));
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}
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#endif
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/* Main Algorithm:
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* every week has 7 days hence, the start of next day would be
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* modulo 7 add to this, the current start date and ensure the
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* result is still modulo 7!
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*/
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start_day = ((days % 7) + start_day) % 7;
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/* If start-day is a Sunday, increment counter */
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if (start_day == 0)
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count_sundays++;
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}
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}
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printf(
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"Total number of Sundays that happened on the 1st of a month in the "
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"last century: %d\n",
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count_sundays);
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return 0;
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}
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