--Lua 5.4.2
local File = io.open("input.txt", "r")

if not File then
    print("File not found")
    return
end

local function IsReportSafe(Numbers)
    local IsSafe = true
    local LastSign = 0
    local LastNumber
    for _, Number in next, Numbers do
        if not LastNumber then
            LastNumber = Number
            goto continue
        end
        local Difference = math.abs(Number - LastNumber)
        if Difference > 3 or Difference == 0 then
            IsSafe = false
            break
        end
        local Sign = (Number - LastNumber) > 0 and 1 or -1
        if LastSign == 0 then
            LastSign = Sign
        else
            if Sign ~= LastSign then
                IsSafe = false
                break
            end
        end
        LastNumber = Number
        ::continue::
    end
    return IsSafe
end

local function Clone(t) --surface level copy
    local Cloned = {}
    for Key, Value in next, t do
        Cloned[Key] = Value
    end
    return Cloned
end

local SafeReports = 0

for Line in File:lines() do
    local Numbers = {}
    for Number in Line:gmatch("%d+") do
        table.insert(Numbers, tonumber(Number))
    end
    if IsReportSafe(Numbers) then
        SafeReports = SafeReports + 1
    else
        for Index = 1, #Numbers do
            local NumbersCopy = Clone(Numbers) --yikes
            table.remove(NumbersCopy, Index)
            if IsReportSafe(NumbersCopy) then
                SafeReports = SafeReports + 1
                break
            end
        end
    end
end

print("Safe reports:", SafeReports)