instantiator / 2021-advent-of-code

Advent of Code, in BBC BASIC.

2021-advent-of-BASIC

Join Advent of Code, complete a puzzle every day in the language of your choice.

I'll be doing it in BBC BASIC - a coding language from a computer called the BBC Micro first released in 1981. Just like me.

Solution code is provided per day, and you can explore each at bbcmic.ro - just copy it in to the editor, and press run.

Notes

Day 3 was the first where the data was too large to operate on in an array. (Well, I could store the data but I couldn't then copy it into an array for random access. I was forced to use it sequentially only.) The workaround: iterating over the input data to build a matching prefix that eventually became the solution.

Day 4 also bumped against several limits of the poor little machine. I had a lot of data, and not enough room to track all the highlighted numbers after each call. I had to get creative, and ended up modifying the cards to remove numbers as they were highlighted.

• Silly mistake: As the scoring works by summing all non-highlighted numbers, I figured I could just zero highlighted numbers - which makes it possible to spot a complete row or column, and very easy to calculate the score of a card. However, 0 is a legitimate number for a board. I had to switch to using -1. (There's no NULL in BBC BASIC.)
• Silly mistake: I was waiting for a board to have a row AND a column. Should have been OR.
• Silly mistake: Bingo cards can only win once!