84 lines
2.1 KiB
JavaScript
84 lines
2.1 KiB
JavaScript
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import { readFileSync } from 'node:fs';
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const input = readFileSync('input', 'utf-8');
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const moves = input
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.split('\n')
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.filter(line => line)
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.map(line => {
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const [direction, multiplier] = line.split(' ', 2);
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return new Array(parseInt(multiplier)).fill(direction);
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})
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.flat();
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function ropeSimulation(nTailKnots) {
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const positions = [new Array(nTailKnots + 1).fill().map(_ => [0, 0])];
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for (const move of moves) {
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const lastKnots = positions[positions.length - 1];
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let [x, y] = lastKnots[0];
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switch (move) {
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case 'U': y += 1; break;
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case 'D': y -= 1; break;
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case 'L': x -= 1; break;
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case 'R': x += 1; break;
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default: throw new Error('Invalid move');
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}
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const knots = [[x, y]];
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for (let n = 0; n < nTailKnots; n++) {
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([x, y] = knots[knots.length - 1]);
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let [tx, ty] = lastKnots[n + 1];
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if (y === ty && Math.abs(x - tx) === 2) {
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// Horizontal tavel
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tx += (x - tx) / Math.abs(x - tx);
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} else if (x === tx && Math.abs(y - ty) === 2) {
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// Vertical travel
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ty += (y - ty) / Math.abs(y - ty);
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} else if (Math.abs(x - tx) === 2 || Math.abs(y - ty) === 2) {
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// Diagonal travel
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tx += (x - tx) / Math.abs(x - tx);
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ty += (y - ty) / Math.abs(y - ty);
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}
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knots.push([tx, ty]);
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}
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positions.push(knots);
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}
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return positions;
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}
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function countLastKnotPositions(positions) {
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// Count unique positions of tail
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return positions
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.map(position => position[position.length - 1])
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.filter((tailPosition, i, arr) =>
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arr.findLastIndex(tp =>
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tp[0] === tailPosition[0] &&
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tp[1] === tailPosition[1]
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) === i
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)
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.length;
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}
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let positions = ropeSimulation(1);
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const totalPositionsOneKnot = countLastKnotPositions(positions);
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console.log(
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`Total unique positions of tail with 1 knot: ${totalPositionsOneKnot}`
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);
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positions = ropeSimulation(9);
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const totalPositionsTenKnots = countLastKnotPositions(positions);
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console.log(
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`Total unique positions of tail with 10 knots: ${totalPositionsTenKnots}`
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);
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