Best data structure for two way mapping

Question

I want a data structure that maps from key to object and vice-versa(unlike HashMaps that map only in a single direction.) An idea could be to store the HashMap within itself for reverse look-up, but it will be an inefficient approach.

What would be the best implementation for two-way mapping?

Binomial

Take a look at BiMap – Kkt

#13315405 – Buehler

Answer 1

Simplest idea: wrapper class which contains 2 maps, second with swapped keys/values. You will keep O(1) complexity and will use only slightly more memory since you will (probably) keep there reference to object.

Bounty

I mentioned this idea in question itself, but I guess there might be better implementations in terms of efficiency. – Binomial

Why do you think it will be inefficient? You will keep O(1) complexity. – Bounty

@TanaySoni Start simple and only look for inefficiencies when you really need to. Do you have any metrics that would signal this approach as a potential bottleneck in your system? – Rodent

I'm trying to use mapping for pixels in a image processing applications. Considering the large data set( a typical image has millions of pixels), I am looking for a rather efficient approach. – Binomial

@ProblemFactory: Is BitMap implemented the same way? – Binomial

I believe you meant BiMap, then "probably" yes, you can download source and check it by yourself. – Bounty