char[] map = new char[0];
(int X, int Y) size = (0, 0);

public void Input(IEnumerable<string> lines)
{
  map = string.Concat(lines).ToCharArray();
  size = (lines.First().Length, lines.Count());
}

Dictionary<HashSet<(int,int)>,int> areas = new Dictionary<HashSet<(int,int)>,int>();
public void PreCalc()
{
  HashSet<(int, int)> visited = new HashSet<(int, int)>();
  for (int y = 0; y < size.Y; ++y)
    for (int x = 0; x < size.X; ++x)
    {
      var at = (x, y);
      if (visited.Contains(at))
        continue;

      var area = Flood((x, y), visited);
      areas[area.Area] = area.Perim;
    }
}

public void Part1()
{
  int sum = areas.Select(kv => kv.Key.Count * kv.Value).Sum();

  Console.WriteLine($"Fencing total: {sum}");
}
public void Part2()
{
  int sum = areas.Select(kv => kv.Key.Count * countCorners(kv.Key)).Sum();

  Console.WriteLine($"Fencing total: {sum}");
}

readonly (int dX, int dY)[] links = new[] { (1, 0), (0, 1), (-1, 0), (0, -1) };
(HashSet<(int,int)> Area, int Perim) Flood((int X, int Y) from, HashSet<(int X, int Y)> visited)
{
  char at = map[from.Y * size.X + from.X];

  (HashSet<(int,int)> Area, int Perim) ret = (new HashSet<(int,int)>(), 0);
  visited.Add(from);
  ret.Area.Add(from);

  foreach (var link in links)
  {
    (int X, int Y) newAt = (from.X + link.dX, from.Y + link.dY);
    char offset ;
    if (newAt.X < 0 || newAt.X >= size.X || newAt.Y < 0 || newAt.Y >= size.Y)
      offset = '\0';
    else
      offset = map[newAt.Y * size.X + newAt.X];

    if (offset == at)
    {
      if (visited.Contains(newAt))
        continue;

      var nextArea = Flood(newAt, visited);
      ret.Area.UnionWith(nextArea.Area);
      ret.Perim += nextArea.Perim;
    }
    else
    {
      ret.Perim += 1;
    }
  }

  return ret;
}

readonly (int dX, int dY)[] cornerPoints = new[] { (0, 0), (1, 0), (1, 1), (0, 1) };
readonly int[] diagonalValues = new[] { (2 << 0) + (2 << 2), (2 << 1) + (2 << 3) };
int countCorners(HashSet<(int X, int Y)> points)
{
  int corners = 0;
  var bounds = findBounds(points);
  for (int y = bounds.minY - 1; y < bounds.maxY + 1; ++y)
    for (int x = bounds.minX - 1; x < bounds.maxX + 1; ++x)
    {
      var atPoint = cornerPoints.Select(c => points.Contains((x + c.dX, y + c.dY)));
      var before = corners;
      if (atPoint.Where(c => c).Count() % 2 == 1)
        corners++;
      else if (diagonalValues.Contains(atPoint.Select((c, i) => c ? (2 << i) : 0).Sum()))
        corners += 2;
    }

  return corners;
}

(int minX, int minY, int maxX, int maxY) findBounds(HashSet<(int X, int Y)> points)
{
  (int minX, int minY, int maxX, int maxY) ret = (int.MaxValue, int.MaxValue, int.MinValue, int.MinValue);
  foreach (var point in points)
  {
    ret.minX = Math.Min(ret.minX, point.X);
    ret.minY = Math.Min(ret.minY, point.Y);
    ret.maxX = Math.Max(ret.maxX, point.X);
    ret.maxY = Math.Max(ret.maxY, point.Y);
  }

  return ret;
}

List<long> stones = new List<long>();
public void Input(IEnumerable<string> lines)
{
  stones = string.Concat(lines).Split(' ').Select(v => long.Parse(v)).ToList();
}

public void Part1()
{
  var expanded = TryExpand(stones, 25);

  Console.WriteLine($"Stones: {expanded}");
}
public void Part2()
{
  var expanded = TryExpand(stones, 75);

  Console.WriteLine($"Stones: {expanded}");
}

public long TryExpand(IEnumerable<long> stones, int steps)
{
  if (steps == 0)
    return stones.Count();
  return stones.Select(s => TryExpand(s, steps)).Sum();
}
Dictionary<(long, int), long> cache = new Dictionary<(long, int), long>();
public long TryExpand(long stone, int steps)
{
  var key = (stone, steps);
  if (cache.ContainsKey(key))
    return cache[key];

  var result = TryExpand(Blink(stone), steps - 1);
  cache[key] = result;
  return result;
}

public IEnumerable<long> Blink(long stone)
{
  if (stone == 0)
  {
    yield return 1;
    yield break;
  }
  var str = stone.ToString();
  if (str.Length % 2 == 0)
  {
    yield return long.Parse(str[..(str.Length / 2)]);
    yield return long.Parse(str[(str.Length / 2)..]);
    yield break;
  }
  yield return stone * 2024;
}

int[] heights = new int[0];
(int, int) size = (0, 0);

public void Input(IEnumerable<string> lines)
{
  size = (lines.First().Length, lines.Count());
  heights = string.Concat(lines).Select(c => int.Parse(c.ToString())).ToArray();
}

int trails = 0, trailheads = 0;
public void PreCalc()
{
  for (int y = 0; y < size.Item2; ++y)
    for (int x = 0; x < size.Item1; ++x)
      if (heights[y * size.Item1 + x] == 0)
      {
        var unique = new HashSet<(int, int)>();
        trails += CountTrails((x, y), unique);
        trailheads += unique.Count;
      }
}

public void Part1()
{
  Console.WriteLine($"Trailheads: {trailheads}");
}
public void Part2()
{
  Console.WriteLine($"Trails: {trails}");
}

int CountTrails((int, int) from, HashSet<(int,int)> unique)
{
  int found = 0;

  List<(int,int)> toSearch = new List<(int, int)>();
  toSearch.Add(from);

  while (toSearch.Any())
  {
    var cur = toSearch.First();
    toSearch.RemoveAt(0);

    int height = heights[cur.Item2 * size.Item1 + cur.Item1];
    for (int y = -1; y <= 1; ++y)
      for (int x = -1; x <= 1; ++x)
      {
        if ((y != 0 && x != 0) || (y == 0 && x == 0))
          continue;

        var newAt = (cur.Item1 + x, cur.Item2 + y);
        if (newAt.Item1 < 0 || newAt.Item1 >= size.Item1 || newAt.Item2 < 0 || newAt.Item2 >= size.Item2)
          continue;

        int newHeight = heights[newAt.Item2 * size.Item1 + newAt.Item1];
        if (newHeight - height != 1)
          continue;

        if (newHeight == 9)
        {
          unique.Add(newAt);
          found++;
          continue;
        }

        toSearch.Add(newAt);
      }
  }

  return found;
}

int[] layout = new int[0];
public void Input(IEnumerable<string> lines)
{
  layout = string.Join("", lines).ToCharArray().Select(c => int.Parse(c.ToString())).ToArray();
}

public void Part1()
{
  ushort?[] blocks = BuildBlockmap().ToArray();

  var it = 0;
  for (var i = blocks.Length - 1; i > it; i--)
  {
    if (blocks[i] == null)
      continue;

    while (it < blocks.Length && blocks[it] != null)
      ++it;

    if (it >= blocks.Length)
      break;

    (blocks[it], blocks[i]) = (blocks[i], null);
  }

  long checksum = 0;
  foreach (var part in blocks.OfType<ushort>().Select((b, i) => i * b))
    checksum += part;

  Console.WriteLine($"Checksum: {checksum}");
}

public void Part2()
{
  var sparse = BuildSparsemap().ToList();

  for (var i = sparse.Count - 1; i >= 0; i--)
  {
    if (sparse[i].Item1 == null)
      continue;

    for (var j = 0; j < i; ++j)
    {
      if (sparse[j].Item1 != null)
        continue;

      if (sparse[i].Item2 > sparse[j].Item2)
        continue;

      var size = sparse[j].Item2;
      size -= sparse[i].Item2;

      (sparse[j], sparse[i]) = (sparse[i], (null, sparse[i].Item2));

      if (i + 1 < sparse.Count && sparse[i + 1].Item1 == null)
      {
        sparse[i] = (null, (ushort)(sparse[i].Item2 + sparse[i + 1].Item2));
        sparse.RemoveAt(i + 1);
      }

      if (sparse[i - 1].Item1 == null)
      {
        sparse[i - 1] = (null, (ushort)(sparse[i - 1].Item2 + sparse[i].Item2));
        sparse.RemoveAt(i);
      }

      if (size > 0)
        sparse.Insert(j + 1, (null, size));

      j = i + 1;
    }
  }

  int ind = 0;
  long checksum = 0;
  foreach (var (val, cnt) in sparse)
    for (var i = 0; i < cnt; ++i)
    {
      checksum += (val ?? 0) * ind;
      ++ind;
    }

  Console.WriteLine($"Checksum: {checksum}");
}

IEnumerable<ushort?> BuildBlockmap()
{
  ushort blockit = 0;
  bool block = true;
  foreach (var value in layout)
  {
    for (int i = 0; i < value; ++i)
      yield return block ? blockit : null;
    if (block)
      blockit++;
    block = !block;
  }
}

IEnumerable<(ushort?, ushort)> BuildSparsemap()
{
  ushort blockit = 0;
  bool block = true;
  foreach (var value in layout)
  {
    if (block)
      yield return (blockit++, (ushort)value);
    else
      yield return (null, (ushort)value);
    block = !block;
  }
}

public static class LINQExt
{
  public static IEnumerable<(T,T)> PermutatePairs<T>(this IEnumerable<T> source) {
    return source.SelectMany(k => source.Where(v => !v?.Equals(k) ?? false).Select(v => (k, v)));
  }
}

struct Antenna
{
  public int X, Y;
  public char Frequency;
}

List<Antenna> antennae = new List<Antenna>();
int width, height;

public void Input(IEnumerable<string> lines)
{
  char[] map = string.Join("", lines).ToCharArray();
  width = lines.First().Length;
  height = lines.Count();

  for (int y = 0; y < height; ++y)
    for (int x = 0; x < width; ++x)
    {
      char at = map[y * width + x];
      if (at == '.')
        continue;

      antennae.Add(new Antenna{ X = x, Y = y, Frequency = at });
    }
}

public void Part1()
{
  HashSet<(int, int)> antinodes = new HashSet<(int, int)>();

  foreach (var antinode in antennae.GroupBy(k => k.Frequency).SelectMany(g => g.PermutatePairs()).SelectMany(v => GetOpposing(v.Item1, v.Item2)).Where(InRange))
    antinodes.Add(antinode);

  Console.WriteLine($"Unique antinodes: {antinodes.Count}");
}
public void Part2()
{
  HashSet<(int, int)> antinodes = new HashSet<(int, int)>();

  foreach (var antennaePair in antennae.GroupBy(k => k.Frequency).SelectMany(g => g.PermutatePairs()))
  {
    // Iterate separately, to make the handling of bound exit easier
    foreach (var antinode in GetAllOpposing(antennaePair.Item1, antennaePair.Item2).TakeWhile(InRange))
      antinodes.Add(antinode);
    foreach (var antinode in GetAllOpposing(antennaePair.Item2, antennaePair.Item1).TakeWhile(InRange))
      antinodes.Add(antinode);
  }
  Console.WriteLine($"Unique antinodes: {antinodes.Count}");
}

bool InRange((int, int) point) {
  return point.Item1 >= 0 && point.Item1 < width && point.Item2 >= 0 && point.Item2 < height;
}
(int, int)[] GetOpposing(Antenna a, Antenna b) {
  return new[] { (a.X + (a.X - b.X), a.Y + (a.Y - b.Y)), (b.X + (b.X - a.X), b.Y + (b.Y - a.Y)) };
}
IEnumerable<(int, int)> GetAllOpposing(Antenna a, Antenna b) {
  (int, int) diff = (a.X - b.X, a.Y - b.Y);
  (int, int) at = (a.X, a.Y);
  yield return at;

  while (true)
  {
    at.Item1 += diff.Item1;
    at.Item2 += diff.Item2;

    yield return at;
  }
}

List<(long, int[])> data = new List<(long, int[])>();

public void Input(IEnumerable<string> lines)
{
  foreach (var line in lines)
  {
    var parts = line.Split(':', StringSplitOptions.TrimEntries);

    data.Add((long.Parse(parts.First()), parts.Last().Split(' ').Select(int.Parse).ToArray()));
  }
}

public void Part1()
{
  var correct = data.Where(kv => CalcPart(kv.Item1, kv.Item2)).Select(kv => kv.Item1).Sum();

  Console.WriteLine($"Correct: {correct}");
}
public void Part2()
{
  var correct = data.AsParallel().Where(kv => CalcPart2(kv.Item1, kv.Item2)).Select(kv => kv.Item1).Sum();

  Console.WriteLine($"Correct: {correct}");
}

public bool CalcPart(long res, Span<int> num, long carried = 0)
{
  var next = num[0];
  if (num.Length == 1)
    return res == carried + next || res == carried * next;
  return CalcPart(res, num.Slice(1), carried + next) || CalcPart(res, num.Slice(1), carried * next);
}

public bool CalcPart2(long res, Span<int> num, long carried = 0)
{
  var next = num[0];
  // Get the 10 logarithm for the next number, expand the carried value by 10^<next 10log + 1>, add the two together
  // For 123 || 45
  // 45 ⇒ 10log(45) + 1 == 2
  // 123 * 10^2 + 45 == 12345
  long combined = carried * (long)Math.Pow(10, Math.Floor(Math.Log10(next) + 1)) + next;
  if (num.Length == 1)
    return res == carried + next || res == carried * next || res == combined;
  return CalcPart2(res, num.Slice(1), carried + next) || CalcPart2(res, num.Slice(1), carried * next) || CalcPart2(res, num.Slice(1), combined);
}

public struct Point : IEquatable<Point>
{
  public int X { get; set; }
  public int Y { get; set; }

  public Point(int x = 0, int y = 0) {
    X = x;
    Y = y;
  }

  public static Point operator+(Point l, Point r) {
    return new Point(l.X + r.X, l.Y + r.Y);
  }
  public bool Equals(Point other) {
    return X == other.X && Y == other.Y;
  }
}

Point size = new Point(0, 0);
HashSet<Point> obstructions = new HashSet<Point>();
Point guard = new Point(0, 0);

enum Direction
{
  Up = 0,
  Right,
  Down,
  Left
}

public void Input(IEnumerable<string> lines)
{
  size = new Point(lines.First().Length, lines.Count());
  char[] map = string.Join("", lines).ToCharArray();

  for (int y = 0; y < size.Y; ++y)
    for (int x = 0; x < size.X; ++x)
    {
      int pos = y * size.X + x;
      char at = map[pos];
      if (at == '#')
        obstructions.Add(new Point(x, y));
      else if (at == '^')
        guard = new Point(x, y);
    }
}

List<Point> path = new List<Point>();
public void PreCalc()
{
  path = WalkArea().path.Distinct().ToList();
}

public void Part1()
{
  Console.WriteLine($"Visited {path.Count} points");
}
public void Part2()
{
  int loopPoints = path.AsParallel().Where(p => !p.Equals(guard) && WalkArea(p).loop).Count();
  Console.WriteLine($"Valid loop points: {loopPoints}");
}

(IEnumerable<Point> path, bool loop) WalkArea(Point? obstruction = null)
{
  HashSet<(Point, Direction)> loopDetect = new HashSet<(Point, Direction)>();

  Point at = guard;
  Direction dir = Direction.Up;
  while (true)
  {
    if (!loopDetect.Add((at, dir)))
      return (loopDetect.Select(p => p.Item1), true);

    Point next = at;
    switch(dir)
    {
    case Direction.Up: next += new Point(0, -1); break;
    case Direction.Right: next += new Point(1, 0); break;
    case Direction.Down: next += new Point(0, 1); break;
    case Direction.Left: next += new Point(-1, 0); break;
    }

    if (next.X < 0 || next.Y < 0 || next.X >= size.X || next.Y >= size.Y)
      break;
    else if (obstructions.Contains(next) || (obstruction?.Equals(next) ?? false))
      dir = (Direction)(((int)dir + 1) % 4);
    else
      at = next;
  }

  return (loopDetect.Select(p => p.Item1), false);
}

class OrderComparer : IComparer<int>
{
  Dictionary<int, List<int>> ordering;
  public OrderComparer(Dictionary<int, List<int>> ordering) {
    this.ordering = ordering;
  }

  public int Compare(int x, int y)
  {
    if (ordering.ContainsKey(x) && ordering[x].Contains(y))
      return -1;
    return 1;
  }
}

Dictionary<int, List<int>> ordering = new Dictionary<int, List<int>>();
int[][] updates = new int[0][];

public void Input(IEnumerable<string> lines)
{
  foreach (var pair in lines.TakeWhile(l => l.Contains('|')).Select(l => l.Split('|').Select(w => int.Parse(w))))
  {
    if (!ordering.ContainsKey(pair.First()))
      ordering[pair.First()] = new List<int>();
    ordering[pair.First()].Add(pair.Last());
  }
  updates = lines.SkipWhile(s => s.Contains('|') || string.IsNullOrWhiteSpace(s)).Select(l => l.Split(',').Select(w => int.Parse(w)).ToArray()).ToArray();
}

public void Part1()
{
  int correct = 0;
  var comparer = new OrderComparer(ordering);
  foreach (var update in updates)
  {
    var ordered = update.Order(comparer);
    if (update.SequenceEqual(ordered))
      correct += ordered.Skip(ordered.Count() / 2).First();
  }

  Console.WriteLine($"Sum: {correct}");
}
public void Part2()
{
  int incorrect = 0;
  var comparer = new OrderComparer(ordering);
  foreach (var update in updates)
  {
    var ordered = update.Order(comparer);
    if (!update.SequenceEqual(ordered))
      incorrect += ordered.Skip(ordered.Count() / 2).First();
  }

  Console.WriteLine($"Sum: {incorrect}");
}

string wordsearch = "";
int width;
int height;

public void Input(IEnumerable<string> lines)
{
  wordsearch = string.Join("", lines);
  height = lines.Count();
  width = lines.First().Length;
}

public void Part1()
{
  int words = 0;
  for (int y = 0; y < height; y++)
    for (int x = 0; x < width; x++)
      words += SearchFrom(x, y);

  Console.WriteLine($"Words: {words}");
}
public void Part2()
{
  int words = 0;
  for (int y = 1; y < height - 1; y++)
    for (int x = 1; x < width - 1; x++)
      words += SearchCross(x, y);

  Console.WriteLine($"Crosses: {words}");
}

public int SearchFrom(int x, int y)
{
  char at = wordsearch[y * width + x];
  if (at != 'X')
    return 0;

  int words = 0;
  for (int ydir = -1; ydir <= 1; ++ydir)
    for (int xdir = -1; xdir <= 1; ++xdir)
    {
      if (xdir == 0 && ydir == 0)
        continue;

      if (SearchWord(x, y, xdir, ydir))
        words++;
    }

  return words;
}

private readonly string word = "XMAS";
public bool SearchWord(int x, int y, int xdir, int ydir)
{
  int wordit = 0;
  while (true)
  {
    char at = wordsearch[y * width + x];
    if (at != word[wordit])
      return false;

    if (wordit == word.Length - 1)
      return true;

    wordit++;

    x += xdir;
    y += ydir;

    if (x < 0 || y < 0 || x >= width || y >= height)
      return false;
  }
}

public int SearchCross(int x, int y)
{
  if (x == 0 || y == 0 || x == width - 1 || y == width - 1)
    return 0;

  char at = wordsearch[y * width + x];
  if (at != 'A')
    return 0;

  int found = 0;
  for (int ydir = -1; ydir <= 1; ++ydir)
    for (int xdir = -1; xdir <= 1; ++xdir)
    {
      if (xdir == 0 || ydir == 0)
        continue;

      if (wordsearch[(y + ydir) * width + (x + xdir)] != 'M')
        continue;
      if (wordsearch[(y - ydir) * width + (x - xdir)] != 'S')
        continue;

      found++;
    }

  if (found == 2)
    return 1;

  return 0;
}

List<string> instructions = new List<string>();

public void Input(IEnumerable<string> lines)
{
  foreach (var line in lines)
    instructions.AddRange(Regex.Matches(line, @"mul\(\d+,\d+\)|do\(\)|don't\(\)").Select(m => m.Value));
}

public void Part1()
{
  var sum = instructions.Select(mul => Regex.Match(mul, @"(\d+),(\d+)").Groups.Values.Skip(1).Select(g => int.Parse(g.Value))).Select(cc => cc.Aggregate(1, (acc, val) => acc * val)).Sum();
  Console.WriteLine($"Sum: {sum}");
}
public void Part2()
{
  bool enabled = true;
  long sum = 0;
  foreach(var inst in instructions)
  {
    if (inst.StartsWith("don't"))
      enabled = false;
    else if (inst.StartsWith("do"))
      enabled = true;
    else if (enabled)
      sum += Regex.Match(inst, @"(\d+),(\d+)").Groups.Values.Skip(1).Select(g => int.Parse(g.Value)).Aggregate(1, (acc, val) => acc * val);
  }
  Console.WriteLine($"Sum: {sum}");
}

int[][] reports = new int[0][];

public void Input(IEnumerable<string> lines)
{
  reports = lines.Select(l => l.Split(' ').Select(p => int.Parse(p)).ToArray()).ToArray();
}

public void Part1()
{
  int safeCount = reports.Where(report => CheckReport(report)).Count();
  Console.WriteLine($"Safe: {safeCount}");
}
public void Part2()
{
  int safeCount = reports.Where(report => {
    if (CheckReport(report))
      return true;

    for (int i = 0; i < report.Length; ++i)
      if (CheckReport(report.Where((_, j) => j != i)))
        return true;

    return false;
  }).Count();

  Console.WriteLine($"Safe: {safeCount}");
}

bool CheckReport(IEnumerable<int> report)
{
  var diffs = report.SkipLast(1).Zip(report.Skip(1)).Select(v => v.Second - v.First);
  return diffs.All(v => Math.Abs(v) <= 3) && (diffs.All(v => v > 0) || diffs.All(v => v < 0));
}

List<int> _LeftList = new List<int>();
List<int> _RightList = new List<int>();

// Fed via File.ReadLines(...).Select(l => l.Trim())
public void Input(IEnumerable<string> lines)
{
  foreach (var line in lines)
  {
    var split = line.Split(' ', StringSplitOptions.RemoveEmptyEntries).Select(s => int.Parse(s));
    _LeftList.Add(split.First());
    _RightList.Add(split.Last());
  }
}

public void Part1()
{
  Console.WriteLine($"Sum: {_LeftList.Order().Zip(_RightList.Order()).Select(v => Math.Abs(v.First - v.Second)).Sum()}");
}
public void Part2()
{
  Console.WriteLine($"Sum: {_LeftList.Select(l => _RightList.Where(i => i == l).Count() * l).Sum()}");
}