aoc-16.js

const fs = require('fs');

const [OP, A, B, C] = [0, 1, 2, 3];

const samples = fs.readFileSync('input', 'utf-8')
  .split('\n\n')
  .map(cluster => cluster.split('\n'))
  .filter(lines => lines.length === 3)
  .map(lines => {
    return ({
      before: eval(lines[0].split(':')[1]),
      after: eval(lines[2].split(':')[1]),
      code: lines[1].split(' ').map(Number),
    })
  });

const addr = (regs, code) => regs[code[C]] = regs[code[A]] + regs[code[B]];
const addi = (regs, code) => regs[code[C]] = regs[code[A]] + code[B];

const mulr = (regs, code) => regs[code[C]] = regs[code[A]] * regs[code[B]];
const muli = (regs, code) => regs[code[C]] = regs[code[A]] * code[B];

const banr = (regs, code) => regs[code[C]] = regs[code[A]] & regs[code[B]];
const bani = (regs, code) => regs[code[C]] = regs[code[A]] & code[B];

const borr = (regs, code) => regs[code[C]] = regs[code[A]] | regs[code[B]];
const bori = (regs, code) => regs[code[C]] = regs[code[A]] | code[B];

const setr = (regs, code) => regs[code[C]] = regs[code[A]];
const seti = (regs, code) => regs[code[C]] = code[A];

const gtir = (regs, code) => regs[code[C]] = +(code[A] > regs[code[B]]);
const gtri = (regs, code) => regs[code[C]] = +(regs[code[A]] > code[B]);
const gtrr = (regs, code) => regs[code[C]] = +(regs[code[A]] > regs[code[B]]);

const eqir = (regs, code) => regs[code[C]] = +(code[A] === regs[code[B]]);
const eqri = (regs, code) => regs[code[C]] = +(regs[code[A]] === code[B]);
const eqrr = (regs, code) => regs[code[C]] = +(regs[code[A]] === regs[code[B]]);

const allOps = [
  addr, addi,
  mulr, muli,
  banr, bani,
  borr, bori,
  setr, seti,
  gtir, gtri, gtrr,
  eqir, eqri, eqrr
];

const getMatches = sample => 
  allOps.filter((op) => {
    const toModify = [...sample.before];
    op(toModify, sample.code);

    return registersMatch(sample.after, toModify);
  })

const registersMatch = (a, b) => 
    a[0] === b[0] &&
    a[1] === b[1] &&
    a[2] === b[2] &&
    a[3] === b[3];

const opcodes = allOps.map((_, i) => ({
  num: i,
  ops: [...allOps],
}));

samples.forEach((sample) => {
  const matches = getMatches(sample);

  const op = opcodes[sample.code[OP]];

  op.ops = op.ops.filter(fn => matches.includes(fn));
});

let sec = 0;
let found = opcodes.filter(op => op.ops.length === 1);
let notFound = opcodes.filter(op => op.ops.length > 1);
while(found.length < opcodes.length && ++sec < 1000) {
  for(let i = 0; i < notFound.length; ++i) {
    const op = notFound[i];
    op.ops = op.ops.filter(fn => !found.some(foundOp => foundOp.ops.includes(fn)));

    if (op.ops.length === 1) {
      found.push(op)
      notFound.splice(i, 1);
      --i;
    }
  }
}

const ops = opcodes.map(op => op.ops[0]);

const program = fs.readFileSync('input', 'utf-8')
  .split('\n\n')
  .pop()
  .trim()
  .split('\n')
  .map(l => l.split(' ').map(Number));

let regs = [0, 0, 0, 0];
program.forEach(line => ops[line[OP]](regs, line));
console.log(regs);