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https://github.com/parnic/advent-of-code-2024.git
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Day 21
This one was a real doozy. I was all kinds of twisted up trying to find a valid solution here and built + threw away at least 3 implementations that each _almost_ worked.
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272
src/21.cs
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272
src/21.cs
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@ -0,0 +1,272 @@
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using aoc2024.Util;
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namespace aoc2024;
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internal class Day21 : Day
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{
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private List<string> codes = [];
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private static readonly Dictionary<char, ivec2> numericButtonLayout =
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new()
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{
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{'7', new ivec2(0, 0)},
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{'8', new ivec2(1, 0)},
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{'9', new ivec2(2, 0)},
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{'4', new ivec2(0, 1)},
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{'5', new ivec2(1, 1)},
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{'6', new ivec2(2, 1)},
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{'1', new ivec2(0, 2)},
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{'2', new ivec2(1, 2)},
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{'3', new ivec2(2, 2)},
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{'0', new ivec2(1, 3)},
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{'A', new ivec2(2, 3)},
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};
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private static readonly Dictionary<ivec2, char> reverseNumericButtonLayout =
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new()
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{
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{new ivec2(0, 0), '7'},
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{new ivec2(1, 0), '8'},
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{new ivec2(2, 0), '9'},
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{new ivec2(0, 1), '4'},
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{new ivec2(1, 1), '5'},
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{new ivec2(2, 1), '6'},
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{new ivec2(0, 2), '1'},
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{new ivec2(1, 2), '2'},
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{new ivec2(2, 2), '3'},
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{new ivec2(1, 3), '0'},
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{new ivec2(2, 3), 'A'},
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};
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private static readonly Dictionary<char, ivec2> directionalKeypadLayout =
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new()
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{
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{'^', new ivec2(1, 0)},
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{'A', new ivec2(2, 0)},
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{'<', new ivec2(0, 1)},
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{'v', new ivec2(1, 1)},
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{'>', new ivec2(2, 1)},
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};
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private static readonly Dictionary<ivec2, char> reverseDirectionalKeypadLayout =
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new()
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{
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{new ivec2(1, 0), '^'},
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{new ivec2(2, 0), 'A'},
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{new ivec2(0, 1), '<'},
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{new ivec2(1, 1), 'v'},
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{new ivec2(2, 1), '>'},
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};
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private static readonly Dictionary<(char from, char to), List<string>> numericKeypadMoves = GetMoves(numericButtonLayout);
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private static readonly Dictionary<(char from, char to), List<string>> directionalKeypadMoves = GetMoves(directionalKeypadLayout);
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private static readonly Dictionary<(char from, char to), List<string>> allMoves = numericKeypadMoves.Where(k => !directionalKeypadMoves.ContainsKey(k.Key)).Union(directionalKeypadMoves).ToDictionary();
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internal override void Parse()
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{
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codes = [..Util.Parsing.ReadAllLines($"{GetDay()}")];
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}
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private static ivec2? GetPosFromKey(char key, Dictionary<char, ivec2> layout)
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{
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if (!layout.TryGetValue(key, out var pos))
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{
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return null;
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}
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return pos;
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}
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private static char? GetKeyFromPos(ivec2 pos, Dictionary<char, ivec2> layout)
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{
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var dict = reverseDirectionalKeypadLayout;
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if (layout.Count == numericButtonLayout.Count)
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{
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dict = reverseNumericButtonLayout;
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}
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if (!dict.TryGetValue(pos, out var key))
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{
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return null;
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}
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return key;
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}
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private static Dictionary<(char from, char to), List<string>> GetMoves(Dictionary<char, ivec2> keypad)
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{
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var keys = string.Concat(keypad.Select(k => k.Key));
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Dictionary<(char from, char to), List<string>> keypadMoves = [];
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for (int fromIdx = 0; fromIdx < keys.Length; fromIdx++)
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{
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char from = keys[fromIdx];
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var keyPos = GetPosFromKey(from, keypad);
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for (int toIdx = fromIdx; toIdx < keys.Length; toIdx++)
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{
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char to = keys[toIdx];
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var pq = new PriorityQueue<ivec2, int>();
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pq.Enqueue(keyPos!.Value, 0);
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Dictionary<ivec2, (int cost, HashSet<string> options)> state = [];
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state.Add(keyPos.Value, (0, [""]));
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while (pq.TryDequeue(out var pos, out var _))
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{
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var (cost, options) = state[pos];
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if (GetKeyFromPos(pos, keypad) == to)
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{
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keypadMoves.Add((from, to), [.. options]);
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if (from != to)
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{
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HashSet<string> reverseOptions = [];
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foreach (string s1 in options)
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{
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string rev = s1.Reverse()
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.Aggregate("", (current, c) => current + c switch
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{
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'>' => '<',
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'<' => ">",
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'^' => 'v',
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'v' => '^',
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_ => c,
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});
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reverseOptions.Add(rev);
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}
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keypadMoves.Add((to, from), [.. reverseOptions]);
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}
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break;
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}
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foreach (var neighbor in pos.GetBoundedOrthogonalNeighbors(0, 0, keypad.Max(k => k.Value.x), keypad.Max(k => k.Value.y)))
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{
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if (GetKeyFromPos(pos, keypad) == null)
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{
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continue;
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}
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var newCost = cost + 1;
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var hasSeen = state.TryGetValue(neighbor, out var thisState);
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if (!hasSeen)
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{
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thisState = (newCost, []);
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state[neighbor] = thisState;
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}
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if (newCost != thisState.cost)
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{
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continue;
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}
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foreach (string s in options)
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{
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thisState.options.Add(s + ivec2.Sign(neighbor - pos).CharFromDir());
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}
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if (!hasSeen)
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{
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pq.Enqueue(neighbor, newCost);
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}
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}
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}
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}
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}
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return keypadMoves;
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}
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private static List<string> GetSequenceList(string code, Dictionary<(char from, char to), List<string>> keypadMoves)
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{
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List<string> sequence = [""];
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char prevKey = 'A';
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foreach (var key in code)
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{
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var newSeq = new List<string>();
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var moves = keypadMoves[(prevKey, key)];
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foreach (var prevStrokes in sequence)
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{
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foreach (var nextStroke in moves)
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{
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newSeq.Add(prevStrokes + nextStroke + 'A');
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}
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}
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prevKey = key;
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sequence = newSeq;
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}
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return sequence;
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}
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private static long ShortestMovesTo(string current, int level, int stopLevel, Dictionary<(string key, int level), long> cache)
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{
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if (cache.TryGetValue((current, level), out var cost))
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{
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return cost;
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}
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if (level == stopLevel)
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{
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var result = GetSequenceList(current, allMoves).Select(a => a.Length).Min();
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cache.Add((current, level), result);
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return result;
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}
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var firstMoveIdx = current.IndexOf('A');
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var firstMove = current[..(firstMoveIdx + 1)];
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var remainingMoves = current[(firstMoveIdx + 1)..];
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long shortest = long.MaxValue;
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var sequences = GetSequenceList(firstMove, allMoves);
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foreach (var seq in sequences)
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{
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long count = ShortestMovesTo(seq, level + 1, stopLevel, cache);
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if (shortest > count)
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{
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shortest = count;
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}
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}
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if (remainingMoves.Length > 0)
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{
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shortest += ShortestMovesTo(remainingMoves, level, stopLevel, cache);
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}
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cache.Add((current, level), shortest);
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return shortest;
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}
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internal override string Part1()
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{
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var cache = new Dictionary<(string key, int level), long>();
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long total = 0;
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foreach (var code in codes)
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{
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var num = int.Parse(code[..3]);
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var moveLen = ShortestMovesTo(code, 0, 2, cache);
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total += moveLen * num;
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}
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return $"3-level code complexity sum: <+white>{total}";
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}
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internal override string Part2()
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{
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var cache = new Dictionary<(string key, int level), long>();
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long total = 0;
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foreach (var code in codes)
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{
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var num = int.Parse(code[..3]);
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var moveLen = ShortestMovesTo(code, 0, 25, cache);
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total += moveLen * num;
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}
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return $"26-level code complexity sum: <+white>{total}";
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}
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}
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@ -38,6 +38,8 @@ public readonly struct ivec2 : IEquatable<ivec2>, IComparable<ivec2>, IComparabl
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public long ManhattanDistance => Abs(this).Sum;
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public long ManhattanDistanceTo(ivec2 other) => System.Math.Abs(x - other.x) + System.Math.Abs(y - other.y);
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public ivec2 ManhattanVectorTo(ivec2 other) => new(other.x - x, other.y - y);
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public static ivec2 DirFromChar(char ch) => ch switch
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{
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'^' => UP,
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@ -47,6 +49,31 @@ public readonly struct ivec2 : IEquatable<ivec2>, IComparable<ivec2>, IComparabl
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_ => throw new FormatException($"Invalid direction {ch}"),
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};
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public char CharFromDir()
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{
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if (this == UP)
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{
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return '^';
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}
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if (this == RIGHT)
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{
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return '>';
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}
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if (this == LEFT)
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{
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return '<';
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}
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if (this == DOWN)
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{
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return 'v';
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}
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throw new FormatException($"Invalid direction vector {this}");
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}
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public ivec2 GetBestDirectionTo(ivec2 p)
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{
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ivec2 diff = p - this;
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