95 lines
2.6 KiB
C#
95 lines
2.6 KiB
C#
namespace AOC2021;
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/// <summary>
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/// Day 4: <a href="https://adventofcode.com/2021/day/4"/>
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/// </summary>
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public sealed class Day04() : Day(2021, 4, "Giant Squid")
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{
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private List<int>? _call;
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private List<List<int>>? _boards;
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private int _size;
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public override void ProcessInput()
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{
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_call = Input.First().Split(',').Select(int.Parse).ToList();
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_boards = [];
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List<int> currentBoard = [];
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foreach (var line in Input.Skip(2))
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{
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if (string.IsNullOrWhiteSpace(line))
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{
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_boards.Add(currentBoard);
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currentBoard = [];
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continue;
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}
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currentBoard.AddRange(line
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.Split(' ', StringSplitOptions.TrimEntries | StringSplitOptions.RemoveEmptyEntries).Select(int.Parse));
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}
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if (currentBoard.Count != 0) _boards.Add(currentBoard);
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_size = (int)Math.Sqrt(currentBoard.Count);
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}
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public override object Part1()
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{
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int i = _size, b = FirstWin(i);
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while (b == -1)
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{
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i++;
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b = FirstWin(i);
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}
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var called = _call!.Take(i).ToHashSet();
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return called.Last() * _boards![b].Where(x => !called.Contains(x)).Sum();
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}
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public override object Part2()
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{
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Dictionary<int, bool> wonBoards = [];
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for (var i = 0; i < _boards!.Count; i++)
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wonBoards[i] = false;
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var j = _size;
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while (wonBoards.Values.Count(b => b) != wonBoards.Count - 1)
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{
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var c = _call!.Take(j).ToHashSet();
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for (var u = 0; u < _boards.Count; u++)
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wonBoards[u] = HasWin(c, _boards[u]);
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j++;
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}
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var called = _call!.Take(j).ToHashSet();
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var b = wonBoards.Single(kvp => !kvp.Value).Key;
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return called.Last() * _boards[b].Where(x => !called.Contains(x)).Sum();
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}
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private int FirstWin(int i)
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{
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var c = _call!.Take(i).ToHashSet();
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for (var j = 0; j < _boards!.Count; j++)
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if (HasWin(c, _boards[j])) return j;
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return -1;
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}
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private int At(int x, int y) => x * _size + y;
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private bool HasWin(IReadOnlySet<int> c, IReadOnlyList<int> b)
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{
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for (var y = 0; y < _size; y++)
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{
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bool rowWin = true, colWin = true;
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for (var x = 0; x < _size; x++)
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{
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rowWin &= c.Contains(b[At(x, y)]);
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colWin &= c.Contains(b[At(y, x)]);
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}
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if (rowWin || colWin) return true;
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}
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return false;
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}
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}
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