ubunu 18.04 无法安装 npm 解决办法

ubunu 18.04 无法安装npm
提示：

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 npm : Depends: node-gyp (>= 0.10.9) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

使用下面的命令安装

sudo apt install aptitude
sudo aptitude install npm

遇见这个选项：

     Keep the following packages at their current version:
1)     libssl-dev [Not Installed]                         
2)     node-gyp [Not Installed]                           
3)     nodejs-dev [Not Installed]                         
4)     npm [Not Installed]     

Accept this solution? [Y/n/q/?] ?

如果选y，没什么用，先选?再选n就安装成功了，我也不知道为什么

$ npm -v
3.5.2