Ben Ashton
1 year ago
2 changed files with 2083 additions and 0 deletions
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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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