adventofcode/2021/08/part2.mjs
2021-12-08 13:35:19 -05:00

84 lines
2.1 KiB
JavaScript

import fp from "lodash/fp.js";
import _ from "lodash";
import * as p1 from "./part1.mjs";
function decodedDigits(mapping) {
const s = fp.invert(mapping);
return _.flow([
fp.invert,
fp.mapKeys((k) =>
k
.split("")
.map((l) => s[l])
.join("")
),
fp.mapKeys((k) => k.split("").sort().join("")),
])(p1.digits);
}
function guess(unknowns, guessed = {}, inputs) {
const [next] = Object.keys(unknowns);
if (!next) return guessed;
for (const p of unknowns[next]) {
let newUnknowns = fp.mapValues(
(s) => s.filter((x) => x !== p),
fp.omit(next, unknowns)
);
if (Object.values(newUnknowns).some((s) => s.size === 0)) continue;
const r = guess(newUnknowns, { ...guessed, [next]: p }, inputs);
if (!r) continue;
const solution = decodedDigits(r);
if (inputs.every((i) => solution.hasOwnProperty(i.join(""))))
return r;
}
}
export function findMapping(input) {
const values = "abcdefg".split("");
let possibility = Object.fromEntries(values.map((v) => [v, values]));
for (const seq of input) {
const p = Object.values(p1.digits)
.filter((d) => d.length === seq.length)
.join("")
.split("");
for (const l of seq) {
possibility[l] = _.intersection(possibility[l], p);
}
}
// feel cute, might delete later
const one = input.find((i) => i.length === 2);
const seven = input.find((i) => i.length === 3);
const [a] = seven.filter((x) => !one.includes(x));
possibility = fp.mapValues(fp.reject("a"), possibility);
possibility[a] = ["a"];
return guess(possibility, {}, input);
}
export function decodedOutput({ input, output }) {
const mapping = findMapping([...input, ...output]);
const digits = decodedDigits(mapping);
return parseInt(output.map((e) => digits[e.join("")]).join(""));
}
export function solution(input) {
return _.sum(input.map(decodedOutput));
}