ProjectEulerCPP/Source/Problem19.cpp

//ProjectEuler/C++/Source/Problem19.cpp
//Matthew Ellison
// Created: 09-28-18
//Modified: 07-14-19
//How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?
/*
You are given the following information, but you may prefer to do some research for yourself.
1 Jan 1900 was a Monday.
Thirty days has September,
April, June and November.
All the rest have thirty-one,
Saving February alone,
Which has twenty-eight, rain or shine.
And on leap years, twenty-nine.
A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.
*/
//Unless otherwise listed all non-standard includes are my own creation and available from https://bibucket.org/Mattrixwv/myClasses
/*
	Copyright (C) 2019  Matthew Ellison

	This program is free software: you can redistribute it and/or modify
	it under the terms of the GNU Lesser General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU Lesser General Public License for more details.

	You should have received a copy of the GNU Lesser General Public License
	along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/


#include <cinttypes>
#include <string>
#include <sstream>
#include "Stopwatch.hpp"
#include "../Headers/Problem19.hpp"


unsigned int Problem19::START_YEAR = 1901;	//The start year
unsigned int Problem19::END_YEAR = 2000;	//The stop year

Problem19::Problem19() : Problem("How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?"), totalSundays(0){

}

Problem19::DAYS Problem19::getDay(unsigned int month, unsigned int day, unsigned int year){
	//Make sure the numbers are within propper bounds
	if((month < 1) || (month > 12) || (day < 1) || (day > 31) || (year < 1)){
		return ERROR;
	}
	uint64_t numDays = 0;	//The number of days between 01-01-0001 and the date given (Saturday)
	unsigned int currentYear, currentMonth, currentDay;
	currentYear = 1;
	currentMonth = 1;
	currentDay = SATURDAY;
	--day;

	//Add the correct number of days for every year
	while(currentYear < year){
		if(isLeapYear(currentYear)){
			numDays += 366;
		}
		else{
			numDays += 365;
		}
		++currentYear;
	}
	//Add the correct number of days for every month
	while(currentMonth < month){
		//31 day months
		if(currentMonth == 2){
			if(isLeapYear(currentYear)){
				numDays += 29;
			}
			else{
				numDays += 28;
			}
		}
		else if((currentMonth == 1) || (currentMonth == 3) || (currentMonth == 5) || (currentMonth == 7) || (currentMonth == 8) || (currentMonth == 10) || (currentMonth == 12)){
			numDays += 31;
		}
		else{
			numDays += 30;
		}
		++currentMonth;
	}
	//Account for the weird year of 1752
	if(year > 1752){
		numDays -= 11;
	}
	else if(year == 1752){
		if(month > 9){
			numDays -= 11;
		}
		else if(month == 9){
			if(day >= 14){
				numDays -= 11;
			}
			//Days 3-13 were skipped that year
			else if((day > 2) && (day < 14)){
				return ERROR;
			}
		}
	}
	//Add the correct number of days for every day
	numDays += day;

	currentDay += numDays;
	currentDay = currentDay % NUMBER_OF_DAYS;
	switch(currentDay){
		case SUNDAY:	return SUNDAY;
		case MONDAY:	return MONDAY;
		case TUESDAY:	return TUESDAY;
		case WEDNESDAY:	return WEDNESDAY;
		case THURSDAY:	return THURSDAY;
		case FRIDAY:	return FRIDAY;
		case SATURDAY:	return SATURDAY;
		default:		return ERROR;
	}
}

bool Problem19::isLeapYear(unsigned int year){
	if(year < 1){
		return false;
	}
	else if((year % 100) == 0){
		//This rule only applies at and after 1800
		if(year <= 1700){
			return true;
		}
		else if((year % 400) == 0){
			return true;
		}
	}
	else if((year % 4) == 0){
		return true;
	}
	return false;
}

void Problem19::solve(){
	//If the problem has already been solved do nothing and end the function
	if(solved){
		return;
	}

	//Start the timer
	timer.start();

	//Run for all years up to 2000
	for(unsigned int year = START_YEAR;year <= END_YEAR;++year){
		//Run for all months in the year
		for(unsigned int month = 1;month <= 12;++month){
			DAYS day = getDay(month, 1, year);
			if(day == ERROR){
				exit(1);
			}
			else if(day == SUNDAY){
				++totalSundays;
			}
		}
	}

	//Stop the timer
	timer.stop();

	//Throw a flag to show the problem is solved
	solved = true;
}

std::string Problem19::getString() const{
	//If the problem hasn't been solved throw an exception
	if(!solved){
		throw unsolved();
	}
	std::stringstream results;
	results << "There are " << totalSundays << " Sundays that landed on the first of the months from " << START_YEAR << " to " << END_YEAR;
	return results.str();
}

uint64_t Problem19::getTotalSundays() const{
	//If the problem hasn't been solved throw an exception
	if(!solved){
		throw unsolved();
	}
	return totalSundays;
}