Lua

pick.lua

local function pick(rules, count, random_func)
    random_func = random_func or math.random
    count = count or 1
    local ret = {}

    local total_weight = 0
    for _, v in ipairs(rules) do
        local weight = v.weight
        total_weight = total_weight + weight
    end

    if total_weight <= 0 then
        return
    end

    local index
    for i=1, count do
        local rd = random_func(total_weight)
        for k, rule in ipairs(rules) do
            local weight = rule.weight
            if rd <= weight then
                table.insert(ret, rule)
                index = k
                break
            else
                rd = rd - weight
            end
        end
    end
    return ret, index
end

local rules = {
    {
        id=1,
        weight=6000
    },
    {
        id=2,
        weight=3000
    },
    {
        id=3,
        weight=1000
    }
}

pick(rules, 1)

tips.lua

-- 检查一个table是否为空
next(t)