--ProjectEuler/lua/Problem4.lua
--Matthew Ellison
-- Created: 02-05-19
--Modified: 06-19-20
--Find the largest palindrome made from the product of two 3-digit numbers
--All of my requires, unless otherwise listed, can be found at https://bitbucket.org/Mattrixwv/luaClasses
--[[
	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/>.
]]


require "Stopwatch"


local timer = Stopwatch:create();
timer:start();

local palindromes = {};	--Holds all palindromes the program finds
--Loop through every number 100-999 twice, nested, so you can multiply every number by every other number in the array
for num1=100,999 do
	for num2=num1,999 do
		local currentNum = num1 * num2;
		--If the number is a palindrome add it to the list of palindromes, otherwise ignore it
		--Using strings makes it easier to determine a palindrome
		if(tostring(currentNum) == string.reverse(tostring(currentNum))) then
			palindromes[#palindromes+1] = currentNum;
		end
	end
end

--Sort the list for neatness
table.sort(palindromes);

timer:stop();

--Print the results
print("The largest palindrome made from the product of two 3-digit numbers is " .. palindromes[#palindromes]);
print("It took " .. timer:getMilliseconds() .. " milliseconds to run this algorithm");

--[[Results:
The largest palindrome made from the product of two 3-digit numbers is 906609
It took 268.412 milliseconds to run this algorithm
]]