Lua桶排TopK：出现最多的前几项

-- 错误：全表排序取头部，刷新一次排一次
table.sort(words, function(a, b)
    return cnt[a] > cnt[b]
end)

local function topK(words, k)
    local cnt, buckets = {}, {}
    for _, w in ipairs(words) do
        cnt[w] = (cnt[w] or 0) + 1
    end
    for w, c in pairs(cnt) do
        buckets[c] = buckets[c] or {}
        table.insert(buckets[c], w)
    end
    local out = {}
    for c = #words, 1, -1 do
        for _, w in ipairs(buckets[c] or {}) do
            out[#out + 1] = w
            if #out >= k then return out end
        end
    end
    return out
end