Lua队列出队：头指针出队不搬移

-- 错误：每次出队整队前移，高峰期搬移翻倍
function dequeue()
    return table.remove(q, 1)
end

local q, head = {}, 1
local function enqueue(v)
    q[#q + 1] = v
end
local function dequeue()
    if head > #q then
        return nil
    end
    local v = q[head]
    q[head] = nil
    head = head + 1
    return v
end