#!/usr/bin/lua
-- See https://adventofcode.com/2025/day/3

local DEBUG = true

function debug(msg)
	if DEBUG then
		print(msg)
	end
end

function MaxJolt(Battery)
	local b = {}
	local firstdigit = 0
	local seconddigit = 0
	local maxdigit = 0

	lastdigit = tonumber(string.sub(Battery, -1))
	debug("lastdigit " .. lastdigit)

	BatteryNoLast = string.sub(Battery, 0, -2)
	BatteryNoLast:gsub(".", function(c)
		table.insert(b, c)
		return c
	end)

	for key, value in pairs(b) do
		checkdigit = tonumber(value)
		if firstdigit < checkdigit then
			firstdigit = checkdigit
		elseif seconddigit < checkdigit then
			seconddigit = checkdigit
		end
	end
	if seconddigit < lastdigit then
		seconddigit = lastdigit
	end
	debug("First " .. firstdigit)
	debug("Second " .. seconddigit)
	return tostring(firstdigit) .. tostring(seconddigit)
end

function TestMaxJolt(Battery, Test)
	local MJ = MaxJolt(Battery)
	if MJ == Test then
		print("WIN  - " .. Battery .. " " .. MJ .. " == " .. Test)
	else
		print("FAIL - " .. Battery .. " " .. MJ .. " != " .. Test)
	end
end

print("# Self Test")
TestMaxJolt("987654321111111", "98")
TestMaxJolt("811111111111119", "89")
TestMaxJolt("234234234234278", "78")
TestMaxJolt("818181911112111", "89")