Lua区间合并：重叠区间的收拢整理

-- 错误：不合并直接罗列，重叠段各自展示
for _, r in ipairs(ranges) do
    showRange(r)
end

local function mergeRanges(ranges)
    table.sort(ranges, function(a, b)
        return a[1] < b[1]
    end)
    local out = {}
    for _, r in ipairs(ranges) do
        local last = out[#out]
        if last and r[1] <= last[2] then
            last[2] = math.max(last[2], r[2])
        else
            out[#out + 1] = {r[1], r[2]}
        end
    end
    return out
end