function parse(input, gSize = 180) {
const grid = AOC.gInit(gSize, gSize, 0);
const elfGrd = input.split("\n").map((l) => l.split(""));
const mid = Math.floor((gSize - elfGrd.length) / 2);
const elves = [];
for (let r = 0; r < elfGrd.length; r++) {
for (let c = 0; c < elfGrd[0].length; c++) {
if (elfGrd[r][c] === "#") {
grid[r + mid][c + mid] = 1;
elves.push([r + mid, c + mid]);
}
}
}
return [elves, grid];
}
function neighbours(r, c, grid) {
return [
grid[r - 1][c - 1] + grid[r - 1][c] + grid[r - 1][c + 1] > 0,
grid[r + 1][c + 1] + grid[r + 1][c] + grid[r + 1][c - 1] > 0,
grid[r - 1][c - 1] + grid[r][c - 1] + grid[r + 1][c - 1] > 0,
grid[r - 1][c + 1] + grid[r][c + 1] + grid[r + 1][c + 1] > 0
];
}
function round(elves, grid, first) {
const moves = [
[-1, 0],
[1, 0],
[0, -1],
[0, 1]
];
let elvesMoved = 0;
// Find proposed moves
const fTable = new Map();
const nextElves = elves.map(([r, c]) => {
const ns = neighbours(r, c, grid);
const occupiedSides = ns.filter(AOC.identity).length;
if (occupiedSides === 0 || occupiedSides === 4) {
// No neighbours or neighbours on all sides, so stay here
AOC.addToFreqTable(fTable, r + "," + c);
return [r, c];
}
for (let i = first; i < first + 4; i++) {
if (!ns[i % 4]) {
const newPos = AOC.vAdd([r, c], moves[i % 4]);
AOC.addToFreqTable(fTable, newPos[0] + "," + newPos[1]);
return newPos;
}
}
});
// Only move those who don't have a don't have a conflct
for (let i = 0; i < elves.length; i++) {
const [r, c] = elves[i];
const [rNext, cNext] = nextElves[i];
if ((rNext != r || cNext != c) && fTable.get(rNext + "," + cNext) === 1) {
// Only one elf wants this space, so move it
elvesMoved++;
elves[i] = [rNext, cNext];
grid[r][c] = 0;
grid[rNext][cNext] = 1;
}
}
return elvesMoved;
}
function bounds(elves) {
const rows = elves.map(([r, c]) => r);
const cols = elves.map(([r, c]) => c);
return [
[Math.min(...rows), Math.min(...cols)],
[Math.max(...rows), Math.max(...cols)]
];
}
function empty(elves, grid) {
const [[minR, minC], [maxR, maxC]] = bounds(elves);
return (maxR - minR + 1) * (maxC - minC + 1) - AOC.sum(grid.flat().flat());
}
function part1(input) {
const [elves, grid] = parse(input);
for (let i = 0; i < 10; i++) {
round(elves, grid, i % 4);
}
return empty(elves, grid);
}
function part2(input) {
const [elves, grid] = parse(input);
let i = 0;
let elvesMoved;
do {
elvesMoved = round(elves, grid, i % 4);
i++;
} while (elvesMoved !== 0);
return i;
}
Purpose-built for displays of data
Observable is your go-to platform for exploring data and creating expressive data visualizations. Use reactive JavaScript notebooks for prototyping and a collaborative canvas for visual data exploration and dashboard creation.
