AOC2020/aoc2020/lib/aoc20201203.dart

import 'package:aoc2020/aocbase.dart';
import 'package:aoc2020/model/point.dart';
import 'package:aoc2020/model/readdata.dart';

class AOC20201203 extends AOCBase {
  static const tree = '#';

  int indexWrap({int index, int width}) => index % width;
  int treeTest({int index, String line}) {
    var width = line.length;
    var testChar = line[indexWrap(index: index, width: width)];
    return testChar == tree ? 1 : 0;
  }

  int tobogganRide({List<String> hill, Point start, Point slope}) {
    var numberOfTrees = 0;
    var pos = start;
    for (var lineNum = 0; lineNum < hill.length; lineNum += slope.item2) {
      numberOfTrees += treeTest(index: pos.item1, line: hill[lineNum]);
      pos = pos + slope;
    }
    return numberOfTrees;
  }

  @override
  Future<void> a({bool test}) async {
    var filename = (test ?? false) ? classStringTest : classString;
    var mylist = await ReadData.readFileString(filename);
    answerA = tobogganRide(hill: mylist, start: Point(0, 0), slope: Point(3, 1));
  }

  @override
  Future<void> b({bool test}) async {
    var filename = (test ?? false) ? classStringTest : classString;
    var mylist = await ReadData.readFileString(filename);

    var slopes = <Point>[
      Point(1, 1),
      Point(3, 1),
      Point(5, 1),
      Point(7, 1),
      Point(1, 2),
    ];
    answerB = 0;
    for (var slope in slopes) {
      var trees = tobogganRide(hill: mylist, start: Point(0, 0), slope: slope);
      if (answerB == 0) {
        answerB = trees;
      } else {
        answerB *= trees;
      }
    }
  }
}