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+213120202203131334354133550411130050063060344561426462151351261236123301315415324404100140403211313 diff --git a/8/solution.mjs b/8/solution.mjs new file mode 100644 index 0000000..ea855d7 --- /dev/null +++ b/8/solution.mjs @@ -0,0 +1,107 @@ +import { readFileSync } from 'node:fs'; + +const input = readFileSync('input', 'utf-8'); + +// Parse grid +const grid = input + .split('\n') + .filter(line => line) + .map(line => line + .split('') + .filter(c => c) + .map(height => parseInt(height)) + ); + +const w = grid[0]?.length || 0; +const h = grid.length; + +// Confirm grid is complete +for (const row of grid) { + if (row.length !== w) { + throw new Error('Invalid grid row'); + } +} + +// Return an array with the remaining integers after start and up to end +function rest(start, end) { + const steps = Math.abs(start - end); + const mult = start < end ? 1 : -1; + return new Array(steps) + .fill() + .map((_, i) => start + (i + 1) * mult) +} + + +// Calculate the maximum value returned by getHeight when called with a range +// of values from start (non-inclusive) to end +function maxHeight(start, end, getHeight) { + return rest(start, end).reduce( + (max, pos) => Math.max(max, getHeight(pos)), + 0 + ); +} + +// Create a map where each item represents the smallest of the next tallest +// tree in all four directions +const maxMap = grid.map((row, y) => row.map((height, x) => { + const u = maxHeight(y, 0, (pos) => grid[pos][x]); + const d = maxHeight(y, h - 1, (pos) => grid[pos][x]); + const l = maxHeight(x, 0, (pos) => grid[y][pos]); + const r = maxHeight(x, w - 1, (pos) => grid[y][pos]); + + // Return the smallest tree of the tallest trees in each direction + return Math.min(u, r, d, l); +})); + +// Create a map of visible trees +const visibleTrees = grid.map((row, y) => row.map((height, x) => { + // Edge case + if (x === 0 || y === 0 || x === w - 1 || y === h - 1) { + return true; + } + + const obscuredByHeight = maxMap[y][x]; + + return height > obscuredByHeight; +})); + +// Sum visible trees +const totalVisibleTrees = visibleTrees + .flat() + .reduce((total, visible) => total + visible, 0); + +console.log(`The total number of trees visible is: ${totalVisibleTrees}`); + +// Calculate how many trees are visible based on heights returned by getHeight +// for a range of values from start (non-inclusive) to end +function countVisibleTrees(start, end, maxHeight, getHeight) { + let count = 0; + for (const pos of rest(start, end)) { + count++; + if (getHeight(pos) >= maxHeight) { + break; + } + } + return count; +} + +// Calculate the scenic score for a tree +function scenicScore(x, y) { + const maxHeight = grid[y][x]; + const u = countVisibleTrees(y, 0, maxHeight, (pos) => grid[pos][x]); + const d = countVisibleTrees(y, h - 1, maxHeight, (pos) => grid[pos][x]); + const l = countVisibleTrees(x, 0, maxHeight, (pos) => grid[y][pos]); + const r = countVisibleTrees(x, w - 1, maxHeight, (pos) => grid[y][pos]); + + // Return the smallest tree of the tallest trees in each direction + return u * r * d * l; +} + + +// Create a map of scenic scores for all trees +const scenicMap = grid.map((row, y) => row.map((height, x) => + scenicScore(x, y) +)); + +const highestScenicScore = Math.max(...scenicMap.flat()); +console.log(`The highest possible scenic score is: ${highestScenicScore}`);