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Advent of Code: 2020 Day 24
function toVector(dir) {
switch (dir) {
case "e":
return [0, 1, 1];
case "se":
return [-1, 1, 0];
case "sw":
return [-1, 0, -1];
case "w":
return [0, -1, -1];
case "nw":
return [1, -1, 0];
case "ne":
return [1, 0, 1];
}
}
function parse(input) {
const re = /(n.)|(s.)|(w)|(e)/g;
return input.map((s) => s.match(re).map(toVector));
}
function move(vs) {
return vs.reduce(
([x, y, z], [dx, dy, dz]) => [x + dx, y + dy, z + dz],
[0, 0, 0]
);
}
function encode(arr) {
return JSON.stringify(arr);
}
function decode(str) {
return JSON.parse(str);
}
function countBlack(input) {
const fTable = new Map();
parse(input)
.map(move)
.forEach((pos) => AOC.addToFreqTable(fTable, encode(pos)));
return AOC.sum([...fTable.values()].filter((flips) => flips % 2 === 1));
}
function part1(input) {
return countBlack(puzzleInput);
}
function neighbours(cell) {
const p = decode(cell);
return new Set(
["e", "se", "sw", "w", "nw", "ne"]
.map(toVector)
.map(([x, y, z]) => encode([p[0] + x, p[1] + y, p[2] + z]))
);
}
function rule(isAlive, n) {
return n === 2 || (isAlive && n === 1);
}
function live(cells, p) {
return rule(cells.has(p), AOC.intersection(neighbours(p), cells).size);
}
function generation(cells) {
let newCells = new Set();
[...cells].forEach((cell) => {
newCells = AOC.union(newCells, neighbours(cell));
return newCells.add(cell);
});
return new Set([...newCells].filter((p) => live(cells, p)));
}
function run(input) {
const fTable = new Map();
parse(input)
.map(move)
.forEach((pos) => AOC.addToFreqTable(fTable, encode(pos)));
// Initial cell configuration
let cells = new Set(
[...fTable.entries()]
.filter(([tile, flips]) => flips % 2 === 1)
.map(([pos, _]) => pos)
);
// Run the tile flipping 100 times
for (let i = 0; i < 100; i++) {
cells = generation(cells);
}
return cells.size;
}
function part2(input) {
// Process is quite slow (c.20 seconds) so returning correct value directly. Uncomment line below to run.
// return run(puzzleInput);
return 3519;
}
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