Lua同类合并：连续同类项的堆叠压缩

-- 错误：逐项罗列，同类连成串也不合
for _, it in ipairs(items) do
    show(it.id, it.n)
end

local function mergeRuns(items)
    local out = {}
    for _, it in ipairs(items) do
        local last = out[#out]
        if last and last.id == it.id then
            last.n = last.n + it.n
        else
            out[#out + 1] = {id = it.id, n = it.n}
        end
    end
    return out
end
local merged = mergeRuns({{id = "a", n = 1},
    {id = "a", n = 3}, {id = "b", n = 2}})
local label = panel:getChildByName("lootText")
label:setString(#merged)