LuaLFU缓存：频次淘汰的容量治理

local function lfucount(keys)
    local freq = {}
    for _, k in ipairs(keys) do
        freq[k] = (freq[k] or 0) + 1
    end
    return freq
end

local function lfuEvict(keys, cap)
    local freq, order = {}, {}
    for _, k in ipairs(keys) do
        if freq[k] then
            freq[k] = freq[k] + 1
        else
            while #order >= cap do
                local victim, vi, vf =
                    order[1], 1, freq[order[1]]
                for i = 2, #order do
                    if freq[order[i]] < vf then
                        victim = order[i]
                        vi, vf = i, freq[order[i]]
                    end
                end
                table.remove(order, vi)
            end
            freq[k] = 1
            order[#order + 1] = k
        end
    end
    return order
end
local p = getplayerbyname("lfu01")
sendmsg(p, 1, "留存 " .. table.concat(
    lfuEvict({"a", "b", "a", "c"}, 2), ","))