I didn't get through at Google. However, I only asked for 3 weeks to prepare, and I have outside obligations (kids, coaching, that sort of thing). I can easily traverse a binary tree, print all permutations of a set, do DFS and BFS. But I'm not super sharp, especially at a whiteboard.
My review was "not bad, good analysis, but didn't make enough coding progress".
Maybe they were being nice. As I said in another comment, I'm not allowed to know what my scores or reviews were.
FTR, I was a math major, though I did take basic CS algorithms and data structures. So I have a background, but probably further to go than a typical CS major.
I know it will vary by individual, but how many hours, over what period of time, would you say counts as "enough practice" where you might start considering that you probably aren't going to be able to practice enough to do this. Could you ballpark it?
I'd prefer to avoid "unintelligent", but you know, a point at which you'd say, this probably isn't for you, might be time to get some new goals?