Solution to Advent of Code 2020 Day 14 Part 1

AOC_2020_Day14_Part1.js

const { parseInputFile } = require('../utils/parser');

const inputs = parseInputFile('day14-input.txt', /^(mask|mem)(?:\[(\d+)\])? = ([0-9X]+)$/gm)
    .map(([, ins, addr, maskOrValue]) => {
        switch (ins) {
            case 'mask': return {
                ins,
                mask: maskOrValue,
                maskOR: BigInt(parseInt(maskOrValue.replace(/X/g, '0'), 2)),
                maskAND: BigInt(parseInt(maskOrValue.replace(/X/g, '1'), 2))
            };
            case 'mem': return {
                ins,
                addr: BigInt(parseInt(addr)),
                value: BigInt(parseInt(maskOrValue))
            };
            default: throw new Error(`Invalid instruction: ${ ins }`);
        }
    });

/** @type {Map<bigint, bigint>} */
const mem = new Map();
let maskAND = 0n;
let maskOR = 0n;

for (const instruction of inputs) {
    if (instruction.ins === 'mask') {
        maskAND = instruction.maskAND;
        maskOR = instruction.maskOR;

    } else { // can only be "mem" here
        const value = (instruction.value & maskAND) | maskOR;
        mem.set(instruction.addr, value);
    }
}

const part1Answer = Array.from(mem.values()).reduce((total, v) => total + v, 0n);
console.log(`Part 1: ${ part1Answer }`);