99 lines
2.2 KiB
JavaScript
99 lines
2.2 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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function getMap() {
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return input
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.split('\n')
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.filter(line => line)
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.map((line, y) => line
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.split('')
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.map((elevation, x) => {
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const isStart = elevation === 'S';
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const isEnd = elevation === 'E';
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elevation = elevation.replaceAll('S', 'a');
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elevation = elevation.replaceAll('E', 'z');
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const height = elevation.charCodeAt(0) - 97;
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return {
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x,
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y,
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height,
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isStart,
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isEnd,
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path: null
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};
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})
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);
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}
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const cardinals = [
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[0, -1], // North
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[1, 0], // East
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[0, 1], // South
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[-1, 0] // West
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];
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// Recursively walk through map stopping whenever we encounter a square with a
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// shorter path than ours
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function solve(map, x, y, canMoveToSquare, path = []) {
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const square = map[y][x];
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path = [...path, [x, y]];
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if (square.path && square.path.length <= path.length) {
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return;
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}
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square.path = path;
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cardinals
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.map(c => map[y + c[1]]?.[x + c[0]])
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// Filter undefined squares
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.filter(s => s)
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// Filter squares we can't reach
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.filter(s => canMoveToSquare(square, s))
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.forEach(s => solve(map, s.x, s.y, canMoveToSquare, [...path]));
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}
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function shortestPathStartToEnd() {
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const map = getMap();
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const start = map.flat().find(square => square.isStart);
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solve(
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map,
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start.x,
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start.y,
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(from, to) => to.height <= from.height + 1
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);
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const end = map.flat().find(square => square.isEnd);
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return end.path;
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}
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function shortestPathEndToA() {
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const map = getMap();
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const end = map.flat().find(square => square.isEnd);
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solve(
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map,
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end.x,
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end.y,
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(from, to) => to.height >= from.height - 1
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);
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const squareWithShortestDistance = map
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.flat()
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.filter(square => square.path)
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.filter(square => square.height === 0)
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.sort((s1, s2) => s1.path.length - s2.path.length)[0];
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return squareWithShortestDistance.path;
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}
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console.log('This will take a minute...');
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let path;
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path = shortestPathStartToEnd();
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console.log(`The least steps from start to end is: ${path.length - 1}`);
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path = shortestPathEndToA();
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console.log(`The least steps from 'a' to end is: ${path.length - 1}`);
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