local Report = {}
Report.__index = Report

function Report:__tostring ()
    return table.concat(self, ' ')
end

function Report:new (values)
    if #values == 0 then error 'Cannot construct an empty report.' end
    setmetatable(values, Report)
    return values
end

function Report:is_safe_dir (down, allow_dampen)
    local function valid_jump (start, finish)
        local diff = down and start - finish or finish - start
        return diff >= 1 and diff <= 3
    end

    local prev = self[1]
    for i = 2,#self do
        local cur = self[i]

        if valid_jump(prev, cur) then
            prev = cur
        elseif not allow_dampen then
            return false
        else
            local remove_cur = i == #self or valid_jump(prev, self[i+1])

            if not remove_cur then
                local remove_prev = i == 2 or valid_jump(self[i-2], cur)
                if not remove_prev then return false end
                prev = cur
            end

            allow_dampen = false
        end
    end
    return true
end

function Report:is_safe (allow_dampen)
    return self:is_safe_dir(true, allow_dampen) or
        self:is_safe_dir(false, allow_dampen)
end

local input = {}

for line in function () return io.read('*l') end do
    local parsed = {}
    for v in line:gmatch('%d+') do
        table.insert(parsed, tonumber(v))
    end
    table.insert(input, Report:new(parsed))
end

function input:sum_safe (allow_dampen)
    local sum = 0
    for _, x in ipairs(input) do
        if x:is_safe(allow_dampen) then sum = sum + 1 end
    end
    return sum
end

function input:part1 ()
    print(self)
    print(self:sum_safe(false))
end

function input:part2 ()
    print(self:sum_safe(true))
end

return input