108 lines
3.0 KiB
JavaScript
108 lines
3.0 KiB
JavaScript
import { readFileSync } from 'node:fs';
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const input = readFileSync('input', 'utf-8');
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// Parse grid
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const grid = input
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.split('\n')
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.filter(line => line)
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.map(line => line
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.split('')
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.filter(c => c)
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.map(height => parseInt(height))
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);
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const w = grid[0]?.length || 0;
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const h = grid.length;
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// Confirm grid is complete
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for (const row of grid) {
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if (row.length !== w) {
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throw new Error('Invalid grid row');
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}
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}
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// Return an array with the remaining integers after start and up to end
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function rest(start, end) {
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const steps = Math.abs(start - end);
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const mult = start < end ? 1 : -1;
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return new Array(steps)
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.fill()
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.map((_, i) => start + (i + 1) * mult)
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}
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// Calculate the maximum value returned by getHeight when called with a range
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// of values from start (non-inclusive) to end
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function maxHeight(start, end, getHeight) {
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return rest(start, end).reduce(
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(max, pos) => Math.max(max, getHeight(pos)),
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0
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);
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}
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// Create a map where each item represents the smallest of the next tallest
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// tree in all four directions
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const maxMap = grid.map((row, y) => row.map((height, x) => {
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const u = maxHeight(y, 0, (pos) => grid[pos][x]);
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const d = maxHeight(y, h - 1, (pos) => grid[pos][x]);
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const l = maxHeight(x, 0, (pos) => grid[y][pos]);
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const r = maxHeight(x, w - 1, (pos) => grid[y][pos]);
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// Return the smallest tree of the tallest trees in each direction
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return Math.min(u, r, d, l);
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}));
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// Create a map of visible trees
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const visibleTrees = grid.map((row, y) => row.map((height, x) => {
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// Edge case
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if (x === 0 || y === 0 || x === w - 1 || y === h - 1) {
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return true;
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}
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const obscuredByHeight = maxMap[y][x];
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return height > obscuredByHeight;
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}));
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// Sum visible trees
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const totalVisibleTrees = visibleTrees
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.flat()
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.reduce((total, visible) => total + visible, 0);
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console.log(`The total number of trees visible is: ${totalVisibleTrees}`);
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// Calculate how many trees are visible based on heights returned by getHeight
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// for a range of values from start (non-inclusive) to end
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function countVisibleTrees(start, end, maxHeight, getHeight) {
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let count = 0;
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for (const pos of rest(start, end)) {
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count++;
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if (getHeight(pos) >= maxHeight) {
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break;
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}
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}
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return count;
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}
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// Calculate the scenic score for a tree
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function scenicScore(x, y) {
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const maxHeight = grid[y][x];
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const u = countVisibleTrees(y, 0, maxHeight, (pos) => grid[pos][x]);
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const d = countVisibleTrees(y, h - 1, maxHeight, (pos) => grid[pos][x]);
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const l = countVisibleTrees(x, 0, maxHeight, (pos) => grid[y][pos]);
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const r = countVisibleTrees(x, w - 1, maxHeight, (pos) => grid[y][pos]);
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// Return the smallest tree of the tallest trees in each direction
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return u * r * d * l;
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}
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// Create a map of scenic scores for all trees
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const scenicMap = grid.map((row, y) => row.map((height, x) =>
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scenicScore(x, y)
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));
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const highestScenicScore = Math.max(...scenicMap.flat());
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console.log(`The highest possible scenic score is: ${highestScenicScore}`);
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