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Problem20.lua

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+--ProjectEuler/lua/Problem20.lua
+--Matthew Ellison
+-- Created: 03-14-19
+--Modified: 03-28-19
+--What is the sum of the digits of 100!
+--All of my requires, unless otherwise listed, can be found at https://bitbucket.org/Mattrixwv/luaClasses
+--I used the bigint library from https://github.com/empyreuma/bigint.lua
+--[[
+	Copyright (C) 2019  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/>.
+]]
+
+
+require "Stopwatch"
+local bigint = require("bigint")
+
+TOP_NUM = 100;
+
+
+--Start the timer
+timer = Stopwatch:create();
+timer:start();
+
+local num = bigint.new(1);	--The number to be generated
+local sum = 0;	--The sum of the digits in num
+
+for cnt = 1, TOP_NUM do
+	num = bigint.multiply(num, bigint.new(cnt));
+end
+
+--Get a string of the number because it is easier to pull appart the individual characters to get the sum
+numString = bigint.unserialize(num, 's');
+--Run through every character in the string, convert it back to an integer and add it to the running sum
+for cnt = 1, string.len(numString) do
+	sum = sum + tonumber(string.sub(numString, cnt, cnt));
+end
+
+--Stop the timer
+timer:stop()
+
+--Print the results
+io.write("100! = " .. numString .. '\n');
+io.write("The sum of the digits is: " .. sum .. '\n');
+io.write("It took " .. timer:getMilliseconds() .. " milliseconds to run this algorithm\n");
+
+--[[ Results:
+100! = 93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000
+The sum of the digits is: 648
+It took 81.113 milliseconds to run this algorithm
+]]