Added solution to problem 21

src/Problems/Problem21.rs

@@ -0,0 +1,101 @@
+//ProjectEulerRust/src/Problems/Problems21.rs
+//Matthew Ellison
+// Created: 06-17-20
+//Modified: 06-17-20
+//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/RustClasses
+/*
+	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/>.
+*/
+
+
+extern crate myClasses;
+use crate::Problems::Answer::Answer;
+
+pub fn getDescription() -> String{
+	"Evaluate the sum of all the amicable numbers under 10000".to_string()
+}
+
+pub fn solve() -> Answer{
+	let LIMIT = 10000;
+	//Setup the variables
+	let mut divisorSum = Vec::<i64>::new();
+	//Make sure the array is filled with 0's
+	while(divisorSum.len() < LIMIT){
+		divisorSum.push(0);
+	}
+
+	//Start the timer
+	let mut timer = myClasses::Stopwatch::Stopwatch::new();
+	timer.start();
+
+	//Generate the divisors of all numbers < 10000, get their sum, and add it to the list
+	for cnt in 1..LIMIT{
+		let mut divisors = myClasses::Algorithms::getDivisors(cnt as i64);
+		if(divisors.len() > 1){
+			divisors.remove(divisors.len() - 1);
+		}
+		divisorSum[cnt] = divisors.iter().sum();
+	}
+	//Check every sum of divisors in the list for matching sum
+	let mut amicable = Vec::<i64>::new();
+	for cnt in 1..divisorSum.len(){
+		let sum = 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 >= divisorSum.len() as i64){
+			continue;
+		}
+		//We know that divisorSum.at(cnt) == sum, so if divisorSum.at(sum) == cnt we found an amicable number
+		if(divisorSum[sum as usize] == cnt as i64){
+			//A number can't be amicable with itself
+			if(sum == cnt as i64){
+				continue;
+			}
+			//Add it to the array of amicable numbers
+			amicable.push(cnt as i64);
+		}
+	}
+
+	//Stop the timer
+	timer.stop();
+
+	//Sort the array for neatness
+	amicable.sort();
+
+	//Return the results
+	let mut answerString = format!("All amicable numbers less than {} are\n", LIMIT);
+	for cnt in 0..amicable.len(){
+		answerString = format!("{}{}\n", answerString, amicable[cnt]);
+	}
+	answerString = format!("{}The sum of all of these amicable numbers is {}", answerString, amicable.iter().sum::<i64>());
+	return Answer::new(answerString, timer.getString());
+}
+
+/* Results:
+All amicable numbers less than 10000 are
+220
+284
+1184
+1210
+2620
+2924
+5020
+5564
+6232
+6368
+The sum of all of these amicable numbers is 31626
+It took 5.792 milliseconds to solve this problem
+*/