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-- 20q.lua with extended question count
local treeFile = "tree.db"
local monitor = peripheral.find("monitor") or error("No monitor attached!")
monitor.setTextScale(0.5)

local function clear(text)
    monitor.clear()
    monitor.setCursorPos(1, 1)
    for line in text:gmatch("[^\n]+") do
        monitor.write(line)
        local _, y = monitor.getCursorPos()
        monitor.setCursorPos(1, y + 1)
    end
end

local function loadTree()
    if fs.exists(treeFile) then
        local f = fs.open(treeFile, "r")
        local data = textutils.unserialize(f.readAll())
        f.close()
        return data
    else
        return { question = "Is it a living thing?", yes = { guess = "cat" }, no = { guess = "rock" } }
    end
end

local function saveTree(tree)
    local f = fs.open(treeFile, "w")
    f.write(textutils.serialize(tree))
    f.close()
end

local function ask(node, count)
    count = count + 1
    if count == 21 then
        clear("You've hit 20 questions!\nContinue? [y/n]")
        if read():lower():sub(1,1) ~= "y" then
            clear("Giving up early? Maybe next time.\nPress Enter.")
            read()
            return node
        end
    end

    if node.guess then
        clear("Is it a " .. node.guess .. "?\n[y]es / [n]o")
        local reply = read()
        if reply:lower():sub(1,1) == "y" then
            clear("Haha! I got it!\nPress Enter.")
            read()
        else
            clear("Darn! What was it?")
            local correct = read()
            clear("Give a question to split " .. correct .. " vs. " .. node.guess)
            local question = read()
            clear("What's the answer for " .. correct .. "? [y/n]")
            local answer = read():lower():sub(1,1)

            local newNode = { question = question }
            if answer == "y" then
                newNode.yes = { guess = correct }
                newNode.no = node
            else
                newNode.no = { guess = correct }
                newNode.yes = node
            end
            return newNode
        end
    else
        clear(node.question .. "\n[y]es / [n]o")
        local reply = read()
        if reply:lower():sub(1,1) == "y" then
            node.yes = ask(node.yes, count)
        else
            node.no = ask(node.no, count)
        end
    end
    return node
end

while true do
    local tree = loadTree()
    clear("Think of something...\nPress Enter.")
    read()
    tree = ask(tree, 0)
    saveTree(tree)
    clear("Play again? [y/n]")
    if read():lower():sub(1,1) ~= "y" then break end
end