Public
Edited
Dec 16, 2023
Insert cell
Insert cell
Insert cell
function parse(input) {
return input.split("\n").map((row) => row.split(""));
}
Insert cell
Insert cell
function rotate(dir, symbol) {
if (symbol === "╱") {
return [-dir[1], -dir[0]]; // Mirror rotates beam 90 degrees
}
if (symbol === "╲") {
return [dir[1], dir[0]]; // Mirror rotates beam anticlockwise 90 degrees
}
return dir;
}
Insert cell
Insert cell
function energised(mirrors, start = { r: 0, c: 0, dir: [0, 1] }) {
const grid = AOC.gMap(() => 0, mirrors);
const [nRows, nCols] = [grid.length, grid[0].length];
const history = new Set();
const beams = [start];
grid[start.r][start.c] = 1;

while (beams.length > 0) {
const b = beams.shift();
const hash =
b.r * nCols * 9 + b.c * 9 + (b.dir[0] + 1) + (b.dir[1] + 1) * 3;
if (!history.has(hash)) {
history.add(hash);
const mirror = mirrors[b.r][b.c];
b.dir = rotate(b.dir, mirror);
if (mirror === "-" && b.dir[0] !== 0) {
beams.push({ r: b.r, c: b.c, dir: [0, -1] });
b.dir = [0, 1];
} else if (mirror === "|" && b.dir[1] !== 0) {
beams.push({ r: b.r, c: b.c, dir: [1, 0] });
b.dir = [-1, 0];
}

const [r, c] = [b.r + b.dir[0], b.c + b.dir[1]];
if (r >= 0 && c >= 0 && r < nRows && c < nCols) {
grid[r][c] = 1;
beams.push({ r: r, c: c, dir: b.dir });
}
}
}
return AOC.sum(grid.flat());
}
Insert cell
function part1(input) {
return energised(parse(puzzleInput));
}
Insert cell
Insert cell
Insert cell
Insert cell
Insert cell
function maxEnergised(mirrors) {
const [nRows, nCols] = [mirrors.length, mirrors[0].length];
let maxE = 0;

for (let r = 0; r < nRows; r++) {
maxE = Math.max(
maxE,
energised(mirrors, { r: r, c: 0, dir: [0, 1] }),
energised(mirrors, { r: r, c: nCols - 1, dir: [0, -1] })
);
}

for (let c = 1; c < nCols - 1; c++) {
maxE = Math.max(
maxE,
energised(mirrors, { r: 0, c: c, dir: [1, 0] }),
energised(mirrors, { r: nRows - 1, c: c, dir: [-1, 0] })
);
}
return maxE;
}
Insert cell
function part2(input) {
return maxEnergised(parse(input));
}
Insert cell
Insert cell
Insert cell
Insert cell
Insert cell
Insert cell
Insert cell
Insert cell
Insert cell

One platform to build and deploy the best data apps

Experiment and prototype by building visualizations in live JavaScript notebooks. Collaborate with your team and decide which concepts to build out.
Use Observable Framework to build data apps locally. Use data loaders to build in any language or library, including Python, SQL, and R.
Seamlessly deploy to Observable. Test before you ship, use automatic deploy-on-commit, and ensure your projects are always up-to-date.
Learn more