Answer to: How to choose between brute force and efficient solution that has overhead?

I know that the most efficient way of doing this is an Approximate nearest neighbor search (ANN) but as far as I can tell all ANN algorithms have overhead One thing that you will need to do to make sense of this is to distinguish between space and time costs. There's often a tradeoff between the amount of memory required for an algorithm and its performance in terms of time. You need to consider these costs separately in order to get anywhere. For example, you might find an approach with excellent performance but the memory required exceeds what you can have or can afford. Another aspect of this to consider is there are different kinds of time complexity and which kind matters depends on your specific constraints and requirements.