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day6.dart
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day6.dart
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import 'dart:io';
class Day6 {
final File _input = File('./input/day6.txt');
Future<List<String>> get _inputLines => _input.readAsLines();
Future<int> part1() async {
List<Race> games = await parseGames();
return games.map(getWinHoldTimes).map((e) => e.length).reduce((value, element) => value * element);
}
Future<int> part2() async {
Race race = await parseGame();
return getWinHoldTimes(race).length;
}
Future<List<Race>> parseGames() async {
final List<String> inputLines = await _inputLines;
final timeStr = inputLines[0].replaceFirst('Time:', '').trim();
final distanceStr = inputLines[1].replaceFirst('Distance:', '').trim();
List<int> timeArr = timeStr.split(RegExp('\\s+')).map((e) => int.parse(e)).toList();
List<int> distanceArr = distanceStr.split(RegExp('\\s+')).map((e) => int.parse(e)).toList();
List<Race> games = [];
for (int i = 0; i < timeArr.length; i++) {
games.add((timeMs: timeArr[i], recordMm: distanceArr[i]));
}
return games;
}
Future<Race> parseGame() async {
final List<String> inputLines = await _inputLines;
final timeStr = inputLines[0].replaceFirst('Time:', '').replaceAll(RegExp('\\s+'), '');
final distanceStr = inputLines[1].replaceFirst('Distance:', '').replaceAll(RegExp('\\s+'), '');
return (timeMs: int.parse(timeStr), recordMm: int.parse(distanceStr));
}
}
typedef Race = ({int timeMs, int recordMm});
List<int> getWinHoldTimes(Race race) {
int velocityCharge = 1; // mm/ms
List<int> holdTimes = [];
for (int i = 0; i < race.timeMs; i++) {
int holdTimeMs = i;
int velocity = holdTimeMs * velocityCharge;
int movingTimeMs = race.timeMs - holdTimeMs;
int distanceMm = movingTimeMs * velocity;
if (distanceMm > race.recordMm) {
holdTimes.add(holdTimeMs);
} else if (holdTimes.isNotEmpty) {
break;
}
}
return holdTimes;
}