Public
Edited
Dec 23, 2022
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 empty(elves, grid) {
const eRows = elves.map(([r, c]) => r);
const eCols = elves.map(([r, c]) => c);
const [minRow, maxRow] = [Math.min(...eRows), Math.max(...eRows)];
const [minCol, maxCol] = [Math.min(...eCols), Math.max(...eCols)];
return (
(maxRow - minRow + 1) * (maxCol - minCol + 1) - AOC.sum(grid.flat().flat())
);
}
part1 = {
const [elves, grid] = parse(input);
for (let i = 0; i < 10; i++) {
round(elves, grid, i % 4);
}
return empty(elves, grid);
}
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