Day 3 - Rucksack Reorganisation

See Day 3 for a detailed description of the problem.

Continuing to solve the Advent of Code 2022 problems (see Advent of Code - Day 1).

Links:

To run the example code in this post save the code into file such as advent.jactl and take your input from the Advent of Code site (e.g. advent.txt) and run it like this:

$ cat advent.txt | java -jar jactl-2.1.0.jar advent.jactl

Part 1

Part 1 involved splitting each input line in half and then finding which letters were in common between the two halves and then generating a “priority” score for the letter (a-z: 1-26, A-Z:27-52) and summing the priorities of these common letters.

The only difficulty was remembering to filter out duplicates.

stream(nextLine).flatMap{
                   def half1 = it.substring(0,it.size()/2);
                   def half2 = it.substring(it.size()/2);
                   half1.filter{ it in half2 }.sort().unique()
                 }
                .map{ /[a-z]/r ? (int)it - (int)'a' + 1 : (int)it - (int)'A' + 27 }
                .sum()

Part 2

For part 2 we have to group the input lines into sets of 3 and find the letter in common across each set of 3 lines and then sum their priorities as before.

Using the grouped() method which groups sets of consecutive elements into a series of lists, this turned out to be fairly simple to implement.

stream(nextLine).grouped(3)
                .flatMap{ a,b,c -> a.filter{ it in b && it in c }.sort().unique() }
                .map{ /[a-z]/r ? (int)it - (int)'a' + 1 : (int)it - (int)'A' + 27 }
                .sum()