Added solution to problem 21

ProblemSelection.ts

@@ -44,11 +44,12 @@ import { Problem17 } from "./Problems/Problem17";
 import { Problem18 } from "./Problems/Problem18";
 import { Problem19 } from "./Problems/Problem19";
 import { Problem20 } from "./Problems/Problem20";
+import { Problem21 } from "./Problems/Problem21";
 
 
 export class ProblemSelection{
 	//Holds the valid problem numbers
-	public static PROBLEM_NUMBERS: number[] = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20];
+	public static PROBLEM_NUMBERS: number[] = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21];
 
 	//Returns the problem corresponding to the given problem number
 	public static getProblem(problemNumber: number): Problem{
@@ -74,6 +75,7 @@ export class ProblemSelection{
 			case 18: problem = new Problem18(); break;
 			case 19: problem = new Problem19(); break;
 			case 20: problem = new Problem20(); break;
+			case 21: problem = new Problem21(); break;
 		}
 		return problem;
 	}

Problems/Problem20.ts

@@ -1,4 +1,4 @@
-//ProjectEulerTS/Problems/Problem19.ts
+//ProjectEulerTS/Problems/Problem20.ts
 //Matthew Ellison
 // Created: 04-07-21
 //Modified: 04-07-21

Problems/Problem21.ts

@@ -0,0 +1,142 @@
+//ProjectEulerTS/Problems/Problem21.ts
+//Matthew Ellison
+// Created: 04-08-21
+//Modified: 04-08-21
+//Evaluate the sum of all the amicable numbers under 10000
+//Unless otherwise listed all non-standard includes are my own creation and available from https://bibucket.org/Mattrixwv/typescriptClasses
+/*
+	Copyright (C) 2021  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/>.
+*/
+
+
+import { getDivisors, getSum } from "../../../Typescript/typescriptClasses/Algorithms";
+import { Unsolved } from "../Unsolved";
+import { Problem } from "./Problem";
+
+
+export class Problem21 extends Problem{
+	//Variables
+	//Static variables
+	private static LIMIT: number = 10000;	//The number that is > the largest number to be checked
+	//Instance variables
+	private divisorSum: number[];	//Holds the sum of the divisors of the subscript number
+	private amicable: number[];	//Holds all amicable numbers
+
+	//Functions
+	//Constructor
+	public constructor(){
+		super(`Evaluate the sum of all the amicable numbers under ${Problem21.LIMIT}`);
+		this.divisorSum = [];
+		this.amicable = [];
+		this.reserveArray();
+	}
+	//Operational functions
+	//Reserve the size of the array to speed up insertion
+	private reserveArray(): void{
+		//Reserving it now makes it faster later
+		//Make sure the array is filled with 0's
+		while(this.divisorSum.length < Problem21.LIMIT){
+			this.divisorSum.push(0);
+		}
+	}
+	//Solve the problem
+	public solve(): void{
+		//If the problem has already been solved do nothing and end the function
+		if(this.solved){
+			return;
+		}
+
+		//Start the timer
+		this.timer.start();
+
+		//Generate the divisors of all numbers < 10000, get their sum, and add it to the list
+		for(let cnt = 1;cnt < Problem21.LIMIT;++cnt){
+			let divisors: number[] = getDivisors(cnt);	//Get all the divisors of a number
+			if(divisors.length > 1){
+				divisors.pop();	//Remove the last element because it will be the number itself
+			}
+			this.divisorSum[cnt] = getSum(divisors);
+		}
+		//Check every sum of divisors in the list for matching sum
+		for(let cnt = 1;cnt < this.divisorSum.length;++cnt){
+			let sum: number = this.divisorSum[cnt];
+			//If the sum is greater than the number of divisors then it is impossible to be amicable. Skip the number and continue
+			if(sum >= this.divisorSum.length){
+				continue;
+			}
+			//We know that divisorSum[cnt] == sum, so if divisorSum[sum] == cnt we found an amicable number
+			if(this.divisorSum[sum] == cnt){
+				//A number can't be amicable with itself
+				if(sum == cnt){
+					continue;
+				}
+				//Add it to the array of amicable numbers
+				this.amicable.push(cnt);
+			}
+		}
+
+		//Sort the array for neatness
+		this.amicable.sort((n1, n2) => n1 - n2);
+
+		//Stop the timer
+		this.timer.stop();
+
+		//Throw a flag to show the problem is solved
+		this.solved = true;
+	}
+	//Reset the problem so it can be run again
+	public reset(): void{
+		super.reset();
+		this.divisorSum = [];
+		this.amicable = [];
+		this.reserveArray();
+	}
+	//Gets
+	//Returns the result of solving the problem
+	public getResult(): string{
+		if(!this.solved){
+			throw new Unsolved();
+		}
+		let result: string = `All amicable numbers less than ${Problem21.LIMIT} are\n`;
+		for(let cnt = 0;cnt < this.amicable.length;++cnt){
+			result += `${this.amicable[cnt]}\n`;
+		}
+		result += `The sum of all of these amicable numbers is ${getSum(this.amicable)}`;
+
+		return result;
+	}
+	//Returns a vector with all of the amicable numbers calculated
+	public getAmicable(): number[]{
+		//If the problem hasn't been solved throw an exception
+		if(!this.solved){
+			throw new Unsolved();
+		}
+		return this.amicable;
+	}
+	//Returns the sum of all of the amicable numbers
+	public getSum(): number{
+		//If the problem hasn't been solved throw an exception
+		if(!this.solved){
+			throw new Unsolved();
+		}
+		return getSum(this.amicable);
+	}
+}
+
+/* Results:
+The sum of all of these amicable numbers is 31626
+It took an average of 7.454 milliseconds to run this problem through 100 iterations
+*/