【高级技巧】多重映射：一键多值的分组存储

local multimap = {}
local function add(key, value)
    local list = multimap[key]
    if not list then
        list = {}
        multimap[key] = list
    end
    list[#list + 1] = value
end
local function remove(key, value)
    local list = multimap[key]
    if not list then
        return
    end
    for i, v in ipairs(list) do
        if v == value then
            table.remove(list, i)
            if #list == 0 then
                multimap[key] = nil
            end
            return
        end
    end
end

add("裁决之杖", "玛法老玩家")
add("裁决之杖", "沙城老兵")
add("骨玉权杖", "玛法老玩家")
remove("裁决之杖", "玛法老玩家")
print(#multimap["裁决之杖"])