Day 1

The input looks like:

The problem is doing a sum of the numbers, grouped by the new line separations (so, here, 100+200+300, 400, 500+600). Then comes the easy part: you have to get the highest number for part one, then the sum of the top three for part two of the puzzle.

First I thought I could do it in Python, picking all items per row and appending them to a new list until it reaches an empty line, so that you get something easy to sum. The result to sum would be something like:

[100,200,300]
[400]
[500,600]

But then I thought, what the hell, doing it in a Bash oneliner is much more entertaining. I didn’t want to write a full script for what felt like a menial task. My first thought was to divide the output in columns - maybe something like:

100,400,500
200,,600
300,,

This would be as easy as a sum of all the elements of each column in awk, but it was a bit of a pain to produce with paste or such. Then I realized I just had to transform the new lines into pluses (+), replace any consecutive pluses (++) with new lines (effectively grouping the input) and feed to a calculator (I have a sweet spot for bc). Essentially, I wanted to produce this:

100+200+300
400
500+600

My solution is as simple as tr+sed for some basic character substitutions. From there it’s a matter of sorting and extracting the first item (head) for the requirements of the first half of the puzzle:

tr '\n' '+' < input.txt | sed 's/++/\n/g' | bc | sort -rn | head -1

To get the sum of the top 3, I just modified head and added an awk column sum:

tr '\n' '+' < input.txt | sed 's/++/\n/g' | bc | sort -rn | head -3 | awk '{sum += $1} END {print sum}

And that’s it!