【高级技巧】双端队列：首尾操作的成本差异封装

local function newDeque()
    return { left = {}, right = {} }
end
local function pushRight(d, v)
    d.right[#d.right + 1] = v
end
local function pushLeft(d, v)
    d.left[#d.left + 1] = v
end
local function popLeft(d)
    if #d.left == 0 then
        local n = #d.right
        for i = n, 1, -1 do
            d.left[#d.left + 1] = table.remove(d.right)
        end
    end
    return table.remove(d.left)
end

local dq = newDeque()
pushRight(dq, "任务甲")
pushLeft(dq, "插队任务")
print(popLeft(dq))