AOC 2022 Day 8 - terse version

/// 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)

// ignore_for_file: unused_import
import 'dart:io';

import 'package:collection/collection.dart';
import 'package:more/more.dart';

// 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 = File('data/data08_01.txt').readAsLinesSync();
  var t = DateTime.now();
  print(part1(lines));
  print(part2(lines));
  print('${DateTime.now().difference(t).inMicroseconds} microseconds');
}