段位对局：只与相邻段位同场竞技

-- 错误：全局最近分匹配，跨段凑场
function matchMe(me)
    local best, gap = nil, math.huge
    for _, o in pairs(queue) do
        local d = math.abs(o.score - me.score)
        if d < gap then
            best, gap = o, d
        end
    end
    return best
end

local BUCKET = 200
local function bucketOf(score)
    return math.floor(score / BUCKET)
end
local function matchMe(me)
    local b = bucketOf(me.score)
    for step = 0, 2 do
        local hit = queue[b + step] or queue[b - step]
        if hit then
            return hit, step
        end
    end
    return nil
end