CtCI-6th-Edition | Solutions | Learning library

The problem is as follows: we want to build a wooden board composed of exactly k planks. We're given two types of planks: shorter and longer. How to determine all possible lengths of such a board?

The solution to this problem can be found here.

The pseudocode is:

I would like to append a string in perl within a loop in a fast way, without having to copy the string for each iteration. I'm looking for something like StringBuilder from Java or C#.

I currently know the following alternatives in mind, in order to do 'a += b'.

1. a .= b # concat
2. a = join('', a, b); # join
3. push @a, b # array push

I am not interested in copying all string to the other. I need to copy one character per time, or append small strings foreach iteration. I am trying to solve the following problem: compress the input string 'aaabbccc' to '3a2b3c'. So the idea is to iterate over the input string, check how many repeated characters we have, and then append to the output in the compressed way. What is the most efficient to perform this in perl ?

Here is a link to the problem I was trying to solve. I's slightly different though.