Day 3: Mull It Over

Part 1

Today's task consists of running corrupt multiplication instructions to find out the final total result.

The instructions are only valid when in the format of:

mul(123,4)

This led me to immediately use regex.

To begin I made a parser that would extract all the valid instructions.

function parse(input: string) {
    const regexMatches = input.match(/mul\(\d+,\d+\)/mg);
    return regexMatches?.map(string => string.match(/\d+/mg)?.map(Number));
}

The above parser will take in the whole input string then using regex find the valid multiplication instructions. I next use a map on the matches to further extract the digits within the instruction before returning them as an array of numbers.

[
    [ 338, 323 ], [ 746, 703 ], ...
]

I next created a simple instruction to process the multiplication.

function executeInstruction(input: number[]) {
    return input[0] * input[1];
}

Before finally using a reducer to sum the total executed instructions as per the task's requirements.

const total = parse(input).reduce(
    (sum, instructionData) => sum + executeInstruction(instructionData), 0,
);

Part 2

Part 2 introduces conditional statements, these are do() and don't(). It's also worth noting that only the most recent conditional statement applies to the instruction, with all instructions enabled by default.

To begin I update my regex to now match the new do and don't conditions present. I will then for each regex match, check if it is a do or don't and toggle the enabled boolean as a result. Then when the match is a mul, and enabled is true I perform the same normal behaviour of digit extraction. Finally, the parsed input is returned to the same code as part 1 for a final total to be calculated.

function parse(input: string) {
    // enabled by default
    let enabled = true;
    const results: number[][] = [];
    const regexMatches = input.match(/do\(\)|don't\(\)|mul\(\d+,\d+\)/mg);

    regexMatches.forEach((regexMatch) => {
        if (regexMatch === 'do()') {
            enabled = true;
        }
        else if (regexMatch === 'don\'t()') {
            enabled = false;
        }
        else if (regexMatch.slice(0, 3) === 'mul') {
            if (enabled) {
                // console.log(regexMatch.match(/\d+/mg)?.map(Number));
                results.push(regexMatch.match(/\d+/mg)?.map(Number));
            }
        }
    });
    return results;
}

Below is same as part 1.

function executeInstruction(input: number[]) {
    return input[0] * input[1];
}

const total = parse(input).reduce(
    (sum, instructionData) => sum + executeInstruction(instructionData), 0,
);

This successfully generates the part 2 answer.