【高级技巧】跳表思想：有序榜单的快速插入

local RankBoard = {}
RankBoard.__index = RankBoard
function RankBoard.new(bucketSpan)
    return setmetatable({ span = bucketSpan or 1000,
        buckets = {}, count = 0 }, RankBoard)
end
function RankBoard:insert(name, score)
    local bi = math.floor(score / self.span)
    local b = self.buckets[bi]
    if b == nil then
        b = {}
        self.buckets[bi] = b
    end
    local pos = #b + 1
    for i = 1, #b do
        if b[i].score < score then
            pos = i
            break
        end
    end
    table.insert(b, pos, { name = name, score = score })
    self.count = self.count + 1
end
function RankBoard:topN(n)
    local out = {}
    local keys = {}
    for k in pairs(self.buckets) do
        keys[#keys + 1] = k
    end
    table.sort(keys, function(a, b)
        return a > b
    end
    )
    for _, k in ipairs(keys) do
        for _, e in ipairs(self.buckets[k]) do
            out[#out + 1] = e
            if #out >= n then
                return out
            end
        end
    end
    return out
end

local board = RankBoard.new(1000)
board:insert("兄弟情深", 86500)
board:insert("王者之师", 3210)
local top = board:topN(10)