Advent of Code 2023 Day 10

The long-awaited difficulty spike probably falls tomorrow. Today was simple enough. The input is a comma-separated list like this:

rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7

Part1 simply asks you to evaluate each token with a custom hash function (called HASH, naturally). Part 2 reveals that each token is actually an instruction. There are 256 boxes, each of which can contain several labeled lenses. For each step, calling HASH on the label gives the index of the target box.

{label}={num} means to replace the lens in the target box with {label} with one with focal length {num}. {label}- means to remove the lens with {label} from the target box. Once done, you apply a formula to a lens arrangement to get the answer.

Executing these instructions in code proved fiddly but straightforward.

function arrange(lenses){ 
    let part1 = 0;
    let length = 256;
    let boxes =Array.from(Array(length), () => []); 
    let pattern = /([a-z]+)(-|=)(\d+)?/

    for(lens of lenses){ 
        part1 += HASH(lens);
        let parts = lens.match(pattern);
        let label = parts[1];
        let box = HASH(label);

        if (parts[2] == "-"){ 
            for(let i = 0; i < boxes[box].length; i++){
                //Do nothing if no lens with label in box
                if (boxes[box][i][0] == label){ 
                    boxes[box].splice(i, 1);
                }
            }
        }else{ 
            let done = false;
            let item = [label, parseInt(parts[3])];
            for(let i = 0; i < boxes[box].length; i++){
                //Do nothing if no lens with label in box
                if (boxes[box][i][0] == label){ 
                    boxes[box][i] = item;
                    done = true;
                    break
                }
            }
            if (!done){ 
                boxes[box].push(item);
            }
        }
    }

    return [part1, focusing_power(boxes)];
}