Advent of Code: 2024 Day 18 / Jo Wood

Jo Wood

Professor of Visual Analytics interested in design, geovisualization, visual storytelling and computational thinking.

Workspace

Public

Ξ🎄Advent of Code 2024

Edited

Dec 20

Paused

function parse(input) {

return input.split("\n").map((d) => d.split(",").map(Number));

}

function buildGrid(bytes, size, n = Infinity) {

const grid = AOC.gInit(size, size, true);

bytes.slice(0, n).forEach(([x, y]) => (grid[y][x] = false));

return grid;

}

dirs = [

[-1, 0], // Up

[0, 1], // Right

[1, 0], // Left

[0, -1] // Down

]

function stepsToExit(grid) {

const size = grid.length;

const distances = AOC.gInit(size, size, Infinity);

distances[0][0] = 0;

const queue = [[0, 0]];

while (queue.length > 0) {

const [r, c] = queue.shift();

dirs.forEach(([dr, dc]) => {

const [r1, c1] = [r + dr, c + dc];

if (grid[r1]?.[c1] && distances[r1][c1] > distances[r][c] + 1) {

distances[r1][c1] = distances[r][c] + 1;

queue.push([r1, c1]);

}

});

}

return distances[size - 1][size - 1];

}

function part1(input) {

return stepsToExit(buildGrid(parse(puzzleInput), 71, 1024));

}

function part2(input) {

const bytes = parse(input);

let [left, right] = [0, bytes.length - 1];

while (left <= right) {

const mid = Math.floor((left + right) / 2);

const grid = buildGrid(bytes, 71, mid);

if (stepsToExit(grid) === Infinity) {

right = mid - 1; // Search left

} else {

left = mid + 1; // Search right

}

return `${bytes[right][0]},${bytes[right][1]}`;

}

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