Added solution to problem 23

ProjectEulerCS/ProblemSelection.cs

@@ -32,7 +32,7 @@ namespace ProjectEulerCS{
 		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, 19,
-				 20, 21, 22, 67};
+				 20, 21, 22, 23, 67};
 		public static System.Collections.Generic.List<int> PROBLEM_NUMBERS{
 			get { return _PROBLEM_NUMBERS; }
 		}
@@ -63,6 +63,7 @@ namespace ProjectEulerCS{
 				case 20: problem = new Problem20(); break;
 				case 21: problem = new Problem21(); break;
 				case 22: problem = new Problem22(); break;
+				case 23: problem = new Problem23(); break;
 				case 67: problem = new Problem67(); break;
 			}
 			return problem;

ProjectEulerCS/Problems/Problem23.cs

@@ -0,0 +1,142 @@
+//ProjectEuler/ProjectEulerCS/src/Problems/Problem23.cs
+//Matthew Ellison
+// Created: 09-03-20
+//Modified: 09-03-20
+//Find the sum of all the positive integers which cannot be written as the sum of two abundant numbers
+//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.Collections.Generic;
+
+
+namespace ProjectEulerCS.Problems{
+	public class Problem23 : Problem{
+		//Variables
+		//Static variables
+		private const int MAX_NUM = 28123;	//THe largest number to be checked
+		//Instance variables
+		private List<int> divisorSums;	//This gives the sum of the divisors at subscripts
+		private long sum;	//The sum of all the numbers we are looking for
+		public override string Result{
+			get{
+				if(!solved){
+					throw new Unsolved();
+				}
+				return $"The answer is {sum}";
+			}
+		}
+		public long Sum{
+			get{
+				if(!solved){
+					throw new Unsolved();
+				}
+				return sum;
+			}
+		}
+
+		//Functions
+		//Constructor
+		public Problem23() : base("Find the sum of all the positive integers which cannot be written as the sum of two abundant numbers"){
+			divisorSums = new List<int>();
+			reserveArray();
+			sum = 0;
+		}
+		//Operational functions
+		//Reserve the size of the array to speed up insertion
+		private void reserveArray(){
+			divisorSums.Capacity = MAX_NUM;	//It is faster to reserve the appropriate amount of ram now
+			//Make sure every element has a 0 in it's location
+			while(divisorSums.Count <= MAX_NUM){
+				divisorSums.Add(0);
+			}
+		}
+		//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();
+
+			//Get the sum of the divisors of all numbers < MAX_NUM
+			for(int cnt = 1;cnt < MAX_NUM;++cnt){
+				List<int> div = mee.Algorithms.GetDivisors(cnt);
+				//Remove the last element, which is the number itself. This gives us the propper divisors
+				if(div.Count > 1){
+					div.Remove(div[^1]);
+				}
+				divisorSums[cnt] = mee.Algorithms.GetSum(div);
+			}
+
+			//Get the abundant numbers
+			List<int> abund = new List<int>();
+			for(int cnt = 0;cnt < divisorSums.Count;++cnt){
+				if(divisorSums[cnt] > cnt){
+					abund.Add(cnt);
+				}
+			}
+
+			//Check if each number can be the sum of 2 abundant numbers and add to the sum if no
+			for(int cnt = 1;cnt < MAX_NUM;++cnt){
+				if(!isSum(abund, cnt)){
+					sum += cnt;
+				}
+			}
+
+			//Stop the timer
+			timer.Stop();
+
+			//Throw a flag to show the problem is solved
+			solved = true;
+		}
+		//A function that returns true if num can be created by adding two elements from abund and false if it cannot
+		private bool isSum(List<int> abund, int num){
+			int sum = 0;
+			//Pick a number for the first part of the sum
+			for(int firstNum = 0;firstNum < abund.Count;++firstNum){
+				//Pick a number for the second part of the sum
+				for(int secondNum = firstNum;secondNum < abund.Count;++secondNum){
+					sum = abund[firstNum] + abund[secondNum];
+					if(sum == num){
+						return true;
+					}
+					else if(sum > num){
+						break;
+					}
+				}
+			}
+			//If you have run through the entire list and did not find a sum then it is false
+			return false;
+		}
+		//Reset the problem so it can be run again
+		public override void Reset(){
+			base.Reset();
+			divisorSums.Clear();
+			reserveArray();
+			sum = 0;
+		}
+	}
+}
+
+/* Results:
+The answer is 395424405
+It took an average of 49.876 milliseconds to run this problem through 100 iterations
+*/