Data structure to handle the requirement of following use case

Question

All the records in a database is saved in (key, value) pair formats.Records can always be retrieved by specifying key value. Data structure needs to be developed to handle follo

Answer 1

For 1 and 2, I think Linked Hash Map is a good choice.

For the point 3, an additional Hash map with (digit, position) tuple as key and list of pointers to the values.

Both data structures can be wrapped inside one, and both will point to the same data, of course.