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namespace aoc2021;
/// <summary>
/// Day 4: <see href="https://adventofcode.com/2021/day/4"/>
/// </summary>
public sealed class Day04 : Day
{
private readonly List<int> _call;
private readonly List<List<int>> _boards;
public Day04() : base(4, "Giant Squid")
{
_call = Input.First().Split(',').Select(int.Parse).ToList();
_boards = new();
List<int> currentBoard = new();
foreach (var line in Input.Skip(2))
{
if (string.IsNullOrWhiteSpace(line))
{
_boards.Add(currentBoard);
currentBoard = new();
continue;
}
currentBoard.AddRange(line
.Split(' ', StringSplitOptions.TrimEntries | StringSplitOptions.RemoveEmptyEntries).Select(int.Parse));
}
if (currentBoard.Any()) _boards.Add(currentBoard);
}
public override string Part1()
{
int i = 1, b = FirstWin(i);
while (b == -1)
{
i++;
b = FirstWin(i);
}
var called = _call.Take(i).ToHashSet();
return $"{called.Last() * _boards[b].Where(x => !called.Contains(x)).Sum()}";
}
private int FirstWin(int i)
{
var c = _call.Take(i).ToHashSet();
for (var j = 0; j < _boards.Count; j++)
if (HasWin(c, _boards[j])) return j;
return -1;
}
private static bool HasWin(IReadOnlySet<int> c, IReadOnlyList<int> b) =>
c.Contains(b[0]) && c.Contains(b[1]) && c.Contains(b[2]) && c.Contains(b[3]) && c.Contains(b[4]) ||
c.Contains(b[5]) && c.Contains(b[6]) && c.Contains(b[7]) && c.Contains(b[8]) && c.Contains(b[9]) ||
c.Contains(b[10]) && c.Contains(b[11]) && c.Contains(b[12]) && c.Contains(b[13]) && c.Contains(b[14]) ||
c.Contains(b[15]) && c.Contains(b[16]) && c.Contains(b[17]) && c.Contains(b[18]) && c.Contains(b[19]) ||
c.Contains(b[20]) && c.Contains(b[21]) && c.Contains(b[22]) && c.Contains(b[23]) && c.Contains(b[24]) ||
c.Contains(b[0]) && c.Contains(b[5]) && c.Contains(b[10]) && c.Contains(b[15]) && c.Contains(b[20]) ||
c.Contains(b[1]) && c.Contains(b[6]) && c.Contains(b[11]) && c.Contains(b[16]) && c.Contains(b[21]) ||
c.Contains(b[2]) && c.Contains(b[7]) && c.Contains(b[12]) && c.Contains(b[17]) && c.Contains(b[22]) ||
c.Contains(b[3]) && c.Contains(b[8]) && c.Contains(b[13]) && c.Contains(b[18]) && c.Contains(b[23]) ||
c.Contains(b[4]) && c.Contains(b[9]) && c.Contains(b[14]) && c.Contains(b[19]) && c.Contains(b[24]);
public override string Part2()
{
Dictionary<int, bool> wonBoards = new();
for (var i = 0; i < _boards.Count; i++)
wonBoards[i] = false;
var j = 0;
while (wonBoards.Values.Count(b => b) != wonBoards.Count - 1)
{
var c = _call.Take(j).ToHashSet();
for (var u = 0; u < _boards.Count; u++)
wonBoards[u] = HasWin(c, _boards[u]);
j++;
}
var called = _call.Take(j).ToHashSet();
var b = wonBoards.Single(kvp => !kvp.Value).Key;
return $"{called.Last() * _boards[b].Where(x => !called.Contains(x)).Sum()}";
}
}
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