Question

Suppose you have a sorted List containing server names. You’d like to collapse them as tightly as possible.

Example:

abcd01c, abcd02c, abcd04c, abcd05, z1x

should become

abcd0[1-4]c,abcd05,z1x

What is the simplest algorithm to take care of something like this?

Answer 1

I would store all strings in a prefix map, which makes the decision of a String exists very easy, and also allows fast iteration of a subset of Strings.

Store the Strings as:

(0)abcd01c
(5)     2c, 
(5)     4c, 
(4)    05, 
(0)z1x

The number is the count of characters which have to be taken from the previous String. This is a common implementation for dictionaries like phonebooks, where you have to store many similar Strings.

A Trie is a similar structure, as Brian Roach noticed in the comments.