Advent of Code: 2024 Day 9 / 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 9

Paused

function parse(input) {

return input.split("").map(Number);

}

function defragBlocks(xs) {

const expand = (n, i) => Array(n).fill(i); // Converts a run-length tuple into actual values

const rles = xs.filter((_, i) => !(i % 2)).map((rle, i) => [rle, i]);

const gaps = xs.filter((_, i) => i % 2).reverse(); // Reverse so we can pop off the end

const [out, buffer] = [[], []];

rles.forEach((rle) => {

out.push(expand(...rle));

const gap = gaps.pop();

while (buffer.length < gap) {

buffer.push(...expand(...rles.pop()));

}

out.push(buffer.slice(0, gap));

buffer.splice(0, gap);

});

out.push(buffer); // Empty the buffer if any file blocks left

return d3.sum(out.flat(), (n, i) => n * i);

}

function part1(input) {

return defragBlocks(parse(input));

}

function defragFiles(xs) {

const expand = (n, i) => Array(n).fill(i);

const rles = xs.filter((_, i) => !(i % 2)).map((rle, i) => [rle, i]);

const gaps = xs.filter((_, i) => i % 2).map((gap) => [gap, []]);

for (let i = rles.length - 1; i > 0; i--) {

for (let j = 0; j < i; j++) {

if (rles[i][0] <= gaps[j][0]) {

// We can move the file into a gap

gaps[j][0] -= rles[i][0]; // Shrink the gap

gaps[j][1].push(expand(...rles[i]));

rles[i][1] = 0; // Set the original file block IDs to 0 so ignored by checksum

break;

}

// Interleave files and gaps

const out = [];

for (let j = 0; j < gaps.length; j++) {

out.push(expand(...rles[j]));

out.push(...gaps[j][1]);

out.push(expand(gaps[j][0], 0));

}

return d3.sum(out.flat(), (n, i) => n * i);

}

function part2(input) {

return defragFiles(parse(input));

}

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