Added solution to problem 19

ProjectEulerCS/ProblemSelection.cs

@@ -31,7 +31,8 @@ namespace ProjectEulerCS{
 		//Holds the valid problem numbers
 		private static readonly List<int> _PROBLEM_NUMBERS = new List<int>()
 				{ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9,
-				 10, 11, 12, 13, 14, 15, 16, 17, 18, 67};
+				 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
+				 67};
 		public static System.Collections.Generic.List<int> PROBLEM_NUMBERS{
 			get { return _PROBLEM_NUMBERS; }
 		}
@@ -58,6 +59,7 @@ namespace ProjectEulerCS{
 				case 16: problem = new Problem16(); break;
 				case 17: problem = new Problem17(); break;
 				case 18: problem = new Problem18(); break;
+				case 19: problem = new Problem19(); break;
 				case 67: problem = new Problem67(); break;
 			}
 			return problem;

ProjectEulerCS/Problems/Problem19.cs

@@ -0,0 +1,202 @@
+//ProjectEuler/ProjectEulerCS/src/Problems/Problem19.cs
+//Matthew Ellison
+// Created: 08-26-20
+//Modified: 08-26-20
+//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/CSClasses
+/*
+	Copyright (C) 2020  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/>.
+*/
+
+
+using System;
+
+
+namespace ProjectEulerCS.Problems{
+	public class Problem19 : Problem{
+		//Variables
+		//Static variables
+		//An easier way to signal day of the week
+		private enum DAYS{SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, NUMBER_OF_DAYS, ERROR}
+		private const int START_YEAR = 1901;	//The first year we are going to test
+		private const int END_YEAR = 2000;	//The last year we are going to test
+		//Instance
+		private long totalSundays;	//Keep track of the number of sundays
+
+		//Functions
+		//Constructor
+		public Problem19() : base("How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?"){
+			totalSundays = 0;
+		}
+		//Operational functions
+		//Solve the problem
+		public override void 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 1901-2000
+			for(int year = START_YEAR;year <= END_YEAR;++year){
+				//Run for all months in the year
+				for(int month = 1;month <= 12;++month){
+					DAYS day = GetDay(month, 1, year);
+					if(day == DAYS.ERROR){
+						throw new Exception("There was an error with the day");
+					}
+					else if(day == DAYS.SUNDAY){
+						++totalSundays;
+					}
+				}
+			}
+
+			//Stop the timer
+			_timer.Stop();
+
+			//Throw a flag to show the problem is solved
+			solved = true;
+
+			_result = "There are " + totalSundays + " Sundays that landed on the first of the months from " + START_YEAR + " to " + END_YEAR;
+		}
+		//Return the day of the week that the date you pass into it is on
+		private DAYS GetDay(int month, int day, int year){
+			//Make sure the numbers are within propper bounds
+			if((month < 1) || (month > 12) || (day < 1) || (day > 31) || (year < 1)){
+				return DAYS.ERROR;
+			}
+			int numDays = 0;
+			int currentYear = 1;
+			int currentMonth = 1;
+			int currentDay = (int)DAYS.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
+				switch(currentMonth){
+					case  1:
+					case  3:
+					case  5:
+					case  7:
+					case  8:
+					case 10:
+					case 12: numDays += 31; break;
+					case  4:
+					case  6:
+					case  9:
+					case 11: numDays += 30; break;
+					case  2:
+						if(IsLeapYear(currentYear)){
+							numDays += 29;
+						}
+						else{
+							numDays += 28;
+						}
+						break;
+				}
+				++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)){
+						throw new Exception("Hit 1752 error");
+					}
+				}
+			}
+			//Add the correct number of days for every day
+			numDays += day;
+
+			currentDay += numDays;
+			currentDay %= (int)DAYS.NUMBER_OF_DAYS;
+
+			return currentDay switch{
+				(int)DAYS.SUNDAY => DAYS.SUNDAY,
+				(int)DAYS.MONDAY => DAYS.MONDAY,
+				(int)DAYS.TUESDAY => DAYS.TUESDAY,
+				(int)DAYS.WEDNESDAY => DAYS.WEDNESDAY,
+				(int)DAYS.THURSDAY => DAYS.THURSDAY,
+				(int)DAYS.FRIDAY => DAYS.FRIDAY,
+				(int)DAYS.SATURDAY => DAYS.SATURDAY,
+				(int)DAYS.ERROR => DAYS.ERROR,
+				_ => DAYS.ERROR,
+			};
+		}
+		//Returns true if the year passed to it is a leap year
+		private bool IsLeapYear(int year){
+			if(year < 1){
+				return false;
+			}
+			else if((year % 100) == 0){
+				//This rule only applies at or after 1800
+				if(year <= 1700){
+					return true;
+				}
+				else if((year % 400) == 0){
+					return true;
+				}
+			}
+			else if((year % 4) == 0){
+				return true;
+			}
+			return false;
+		}
+		//Reset the problem so it can be run again
+		public override void Reset(){
+			base.Reset();
+			totalSundays = 0;
+		}
+	}
+}
+
+/* Results:
+There are 171 Sundays that landed on the first of the months from 1901 to 2000
+It took an average of 6.001 milliseconds to run this problem through 100 iterations
+*/