Added solution to problem 20

src/Problems/Problem20.rs

@@ -0,0 +1,65 @@
+//ProjectEulerRust/src/Problems/Problems20.rs
+//Matthew Ellison
+// Created: 06-17-20
+//Modified: 06-17-20
+//What is the sum of the digits of 100!?
+//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{
+	"What is the sum of the digits of 100!?".to_string()
+}
+
+pub fn solve() -> Answer{
+	let TOP_NUM = 100;
+	//The number that is being generated
+	let mut number = num::BigInt::from(1);
+	let mut sum = 0;
+
+	//Start the timer
+	let mut timer = myClasses::Stopwatch::Stopwatch::new();
+	timer.start();
+
+	//Run through every number from 1 to 100 and multiply it by the current num to generate 100!
+	for cnt in (2..=TOP_NUM).rev(){
+		number *= num::BigInt::from(cnt);
+	}
+
+	//Get a string of the number because it is easier to pull apart the individual characters
+	let numString = number.to_string();
+	//Run through every character in the string, convert it back to an integer and add it to the running sum
+	for cnt in numString.chars(){
+		sum += cnt.to_digit(10).unwrap();
+	}
+
+	//Stop the timer
+	timer.stop();
+
+	//Return the results
+	return Answer::new(format!("{}! = {}\nThe sum of the digits is: {}", TOP_NUM, number, sum), timer.getString());
+}
+
+/* Results:
+100! = 93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000
+The sum of the digits is: 648
+It took 18.000 microseconds to solve this problem
+*/