Not that hard depending on your natural cognitive ability. Just grind leetcode questions. For higher level interviews, also study up on systems design questions.
I think that's underselling things. These companies have very low admit rates, and leetcode is pretty tedious. That said though, divide the compensation difference by 200 hours of studying and it probably works out to a worthy investment.
One reason they have very low admit rates because most candidates are absolutely awful and cannot code at all, even if they have years of software development experience! Grinding leetcode is definitely worth it.
