There is no way China wouldn't intervene before a US invasion... And there would be no way they wouldn't know about it in advance, we would have to move hundreds of thousands of troops and all of the logistics for months of operations to that end to South Korea and Japan, which would take at least several weeks, if not several months.

The moment such a move became apparent, China itself would invade North Korea with or without permission under the pretense of preventing the US from invading (and will probably never leave at that point, just taking the country over). So there would be no way for the US to invade without attacking them as well.

If the goal is to simply neutralize North Korea, the best method would be a pre-emptive strike with submarine launched nuclear cruise missiles. But it would be rather difficult to justify a nuclear first strike that kills millions of people to the rest of world, so that's not really an option.

Personally I'd be down with China taking over North Korea, so I'd go with the generic invasion plan to force their hand.