advent-code-2021-day-8.js

function permutate(arr = []) {
  let res = [];
  if (arr.length === 1) {
    return [arr];
  }
  for (let i = 0; i < arr.length; i++) {
    let c = arr[i];
    let rest = arr.slice();
    rest.splice(i, 1);
    permutate(rest).forEach((t) => res.push([c, ...t]));
  }
  return res;
}

let allPermutations = permutate("abcdefg".split(""));

function seqToNum(seq) {
  function p(...ns) {
    return ns.reduce((a, b) => [...a, seq[b]], []);
  }
  const c0 = p(0, 1, 2, 4, 5, 6);
  const c1 = p(2, 5);
  const c2 = p(0, 2, 3, 4, 6);
  const c3 = p(0, 2, 3, 5, 6);
  const c4 = p(1, 2, 3, 5);
  const c5 = p(0, 1, 3, 5, 6);
  const c6 = p(0, 1, 3, 4, 5, 6);
  const c7 = p(0, 2, 5);
  const c8 = p(0, 1, 2, 3, 4, 5, 6);
  const c9 = p(0, 1, 2, 3, 5, 6);
  return [c0, c1, c2, c3, c4, c5, c6, c7, c8, c9].map((seq) => {
    seq.sort();
    return seq.join("");
  });
}

const sequences = allPermutations.map(seqToNum);


// 0:      1:      2:      3:      4:
// aaaa    ....    aaaa    aaaa    ....
// b    c  .    c  .    c  .    c  b    c
// b    c  .    c  .    c  .    c  b    c
// ....    ....    dddd    dddd    dddd
// e    f  .    f  e    .  .    f  .    f
// e    f  .    f  e    .  .    f  .    f
// gggg    ....    gggg    gggg    ....

//  5:      6:      7:      8:      9:
// aaaa    aaaa    aaaa    aaaa    aaaa
// b    .  b    .  .    c  b    c  b    c
// b    .  b    .  .    c  b    c  b    c
// dddd    dddd    ....    dddd    dddd
// .    f  e    f  .    f  e    f  .    f
// .    f  e    f  .    f  e    f  .    f
// gggg    gggg    ....    gggg    gggg

function sortStr(str) {
  return str.split("").sort().join("");
}

function findTheOne(tenOfThem) {
  tenOfThem = tenOfThem.map(sortStr);
  return sequences.find((candidates) => {
    return candidates.every((s) => tenOfThem.includes(s));
  });
}

function run(input = "") {
  const lines = input
    .split("\n")
    .filter(Boolean)
    .map((line) => {
      const [fore, back] = line.split("|");
      return [fore.trim().split(" "), back.trim().split(" ")];
    });

  return lines.reduce((acc, [fore, back]) => {
    const theOne = findTheOne(fore);
    back = back.map(sortStr).map(b => theOne.findIndex(o => o === b))
    back = parseInt(back.join(''));
    return acc + back;
  }, 0);
}

console.log(run(raw));