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December 8, 2022 15:29
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AOC 2022 Day 8 Dart
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/// Given a grid of (real) trees of different heights | |
/// 1) Find how many are visible from any edge | |
/// 2) Find the best view from any trees (= product of distances) | |
import 'package:collection/collection.dart'; | |
//import 'package:more/more.dart'; | |
// Hack for missing `more` library | |
extension IntegerRangeExtension on int { | |
List<int> to(int end) => List.generate(end - this, (i) => i + this); | |
} | |
// Add an offset of 1 to every tree so that 0-height tree work for this hack. | |
List<List<int>> readTrees(List<String> lines) => lines | |
.map((e) => e.split('').map((e) => int.parse(e) + 1).toList()) | |
.toList(); | |
part1(List<String> lines) { | |
var trees = readTrees(lines); | |
// helper function | |
int checkHeight(row, col, targetHeight) { | |
if (trees[row][col].abs() > targetHeight) { | |
targetHeight = trees[row][col].abs(); | |
trees[row][col] = -targetHeight; // <-- means visible! | |
} | |
return targetHeight; | |
} | |
var nCols = trees.first.length, nRows = trees.length; | |
for (var row in 0.to(nRows)) { | |
0.to(nCols).fold(-99, (s, t) => checkHeight(row, t, s)); | |
0.to(nCols).reversed.fold(-99, (s, t) => checkHeight(row, t, s)); | |
} | |
for (var col in 0.to(nCols)) { | |
0.to(nRows).fold(-99, (s, t) => checkHeight(t, col, s)); | |
0.to(nRows).reversed.fold(-99, (s, t) => checkHeight(t, col, s)); | |
} | |
return trees.flattened.where((e) => e < 1).length; | |
} | |
// Part 2 | |
var dirs = [ | |
[0, 1], | |
[0, -1], | |
[1, 0], | |
[-1, 0] | |
]; | |
List<int> viewsFromTree(List<List<int>> trees, List<int> rc) { | |
var row = rc[0], col = rc[1]; | |
inBounds(r, c) => | |
r >= 0 && r < trees.length && c >= 0 && c < trees.first.length; | |
var high = trees[row][col]; | |
var vals = <int>[]; | |
for (var dir in dirs) { | |
var hr = row, hc = col; | |
var val = 0; | |
while (true) { | |
hr += dir[0]; | |
hc += dir[1]; | |
if (!inBounds(hr, hc)) break; | |
val += 1; | |
if (trees[hr][hc] >= high) break; | |
} | |
vals.add(val); | |
} | |
return vals; | |
} | |
part2(List<String> lines) { | |
var trees = readTrees(lines); | |
var rowColPairs = [ | |
for (var row in 0.to(trees.length)) | |
for (var col in 0.to(trees.first.length)) [row, col] | |
]; | |
return rowColPairs.fold( | |
-1, | |
(sofar, rc) => | |
[sofar, viewsFromTree(trees, rc).reduce((s, t) => s * t)].max); | |
} | |
void main(List<String> args) { | |
var lines = data.split('\n'); | |
var t = DateTime.now(); | |
print(part1(lines)); | |
print(part2(lines)); | |
print('${DateTime.now().difference(t).inMicroseconds} microseconds'); | |
} | |
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