I've had to use a binary tree couple of times. And when I did, I recognized the problem as a binary tree problem, and I read up on binary trees, and then used them. For about a month after, I'd have been able to do a lot of tree operations on the spot. Then the the material gradually faded from short term front loaded memory, and my long term memory stored the relevant awareness of the problem so I'd identify it should I have to look it up again.