aoc24/day21/d21p2.swift

import Foundation

typealias Key = String
let (nA, nEmpty) = ("A", "")
let (n7, n8, n9, n4, n5, n6, n1, n2, n3, n0) =
    ("7", "8", "9", "4", "5", "6", "1", "2", "3", "0")
let (nL, nR, nU, nD) = ("<", ">", "^", "v")

protocol Pad {
    static func seq(_ k1: Key, _ k2: Key) -> Set<[Key]>
}

struct KeyPair : Hashable {
    let a: Key
    let b: Key
}

struct Numpad {
    static let pos: [Key: (Int, Int)] = [
        n7: (0, 0), n8: (0, 1), n9: (0, 2),
        n4: (1, 0), n5: (1, 1), n6: (1, 2),
        n1: (2, 0), n2: (2, 1), n3: (2, 2),
                    n0: (3, 1), nA: (3, 2)
    ]
    static var cache: [KeyPair: Set<[Key]>] = [:]

    static func seq(_ k1: Key, _ k2: Key) -> Set<[Key]> {
        let cacheKey = KeyPair(a: k1, b: k2)
        if let cached = cache[cacheKey] {
            return cached
        }
        let (pos1, pos2) = (pos[k1]!, pos[k2]!)
        let verKey = pos1.0 < pos2.0 ? nD : nU
        let horKey = pos1.1 < pos2.1 ? nR : nL
        let seqs: [[Key]] = [  // ???
                Array(repeating: verKey, count: abs(pos1.0 - pos2.0)) +
                Array(repeating: horKey, count: abs(pos1.1 - pos2.1)),
                Array(repeating: horKey, count: abs(pos1.1 - pos2.1)) +
                Array(repeating: verKey, count: abs(pos1.0 - pos2.0))
            ].filter { seq in
                (k1 != n1 || !seq.starts(with: [nD])) &&
                (k1 != n4 || !seq.starts(with: [nD, nD])) &&
                (k1 != n7 || !seq.starts(with: [nD, nD, nD])) &&
                (k1 != n0 || !seq.starts(with: [nL])) &&
                (k1 != nA || !seq.starts(with: [nL, nL]))
            }
        cache[cacheKey] = Set(seqs)
        return cache[cacheKey]!
    }

    static func press(_ start: Key, _ keys: ArraySlice<Key>) -> [[Key]] {
        if keys.count == 0 {
            return [[]]
        }
        return seq(start, keys[keys.startIndex]).flatMap { firstSeq in
                press(keys[keys.startIndex], keys.dropFirst()).map { restSeq in
                    firstSeq + [nA] + restSeq
                }
            }
    }
}

struct Dirpad {
    static let pos: [Key: (Int, Int)] = [
                    nU: (0, 1), nA: (0, 2),
        nL: (1, 0), nD: (1, 1), nR: (1, 2)
    ]
    static var cache: [KeyPair: [Key]] = [
        // <<0 <v- <>- <^. <A.
        // v<- vv0 v>- v^- vA
        // ><- >v- >>0 >^  >A-
        // ^<. ^v- ^>  ^^0 ^A-
        // A<. Av  A>- A^- AA0
        // Noops
        KeyPair(a: nL, b: nL): [],
        KeyPair(a: nR, b: nR): [],
        KeyPair(a: nU, b: nU): [],
        KeyPair(a: nD, b: nD): [],
        KeyPair(a: nA, b: nA): [],
        // Only solutions due to gap
        KeyPair(a: nL, b: nU): [nR, nU],
        KeyPair(a: nL, b: nA): [nR, nR, nU],
        KeyPair(a: nU, b: nL): [nD, nL],
        KeyPair(a: nA, b: nL): [nD, nL, nL],
        // Only solutions
        KeyPair(a: nL, b: nR): [nR, nR],
        KeyPair(a: nR, b: nL): [nL, nL],
        KeyPair(a: nL, b: nD): [nR],
        KeyPair(a: nD, b: nL): [nL],
        KeyPair(a: nU, b: nA): [nR],
        KeyPair(a: nA, b: nU): [nL],
        KeyPair(a: nD, b: nR): [nR],
        KeyPair(a: nR, b: nD): [nL],
        KeyPair(a: nA, b: nR): [nD],
        KeyPair(a: nR, b: nA): [nU],
        KeyPair(a: nU, b: nD): [nD],
        KeyPair(a: nD, b: nU): [nU],
        // Known short ones. TODO: proper DP this part instead of by hand
        KeyPair(a: nA, b: nD): [nL, nD],
        KeyPair(a: nD, b: nA): [nU, nR],
        KeyPair(a: nR, b: nU): [nL, nU],
        KeyPair(a: nU, b: nR): [nD, nR]
    ]

    static func seq(_ k1: Key, _ k2: Key) -> [Key] {
        return cache[KeyPair(a: k1, b: k2)]!
    }

    static func press(_ start: Key, _ keys: ArraySlice<Key>) -> [Key] {
        if keys.count == 0 {
            return []
        }
        return seq(start, keys[keys.startIndex]) + [nA] +
            press(keys[keys.startIndex], keys.dropFirst())
    }
}

func readInput(_ filePath: String) throws -> [[Key]] {
    return try String(contentsOfFile: filePath, encoding: .ascii)
        .split(separator: "\n").map { Array($0).map(String.init) }
}

extension Array {
    func combos(l: Int) -> [[Element]] {
        guard count > 0 else { return [[]] }
        if l == 0 { return [[]] }
        return flatMap { e in
            combos(l: l - 1).map { $0 + [e] }
        }
    }
    func combos(maxl: Int) -> [[Element]] {
        return (0...maxl).flatMap { combos(l: $0) }
    }
}

struct LKs : Hashable {
    let l: Int
    let ks: [Key]
}

// Returns a map of a sequence of pressed starting at A and ending at A
// to how many key presses total for that
func bestLevel1() -> [LKs: Int] {
    var res: [LKs: Int] = [:]
    [nL, nR, nU, nD].combos(maxl: 3).forEach { seq in
        res[LKs(l: 1, ks: seq)] = Dirpad.press(nA, seq + [nA]).count
    }
    return res
}
func best(maxLevel: Int) -> [LKs: Int] {
    var res = bestLevel1()
    if maxLevel == 1 { return res }
    (2...maxLevel).forEach { level in
        [nL, nR, nU, nD].combos(maxl: 3).forEach { seq in
            res[LKs(l: level, ks: Array(seq))] = Dirpad.press(nA, seq + [nA])
                .split(separator: "A", omittingEmptySubsequences: false).dropLast()
                .map { res[LKs(l: level-1, ks: Array($0))]! }.reduce(0, +)
        }
    }
    return res
}

let levels = Int(CommandLine.arguments[2])! - 1
let bests = best(maxLevel: levels)

var answer = 0
for passwd in try readInput(CommandLine.arguments[1]) {
    let n = Numpad.press(nA, passwd[...])
        .map { Dirpad.press(nA, $0[...]) }.map { ks in
            return ks
                .split(separator: "A", omittingEmptySubsequences: false).dropLast()
                .map { bests[LKs(l: levels, ks: Array($0))]! }
                .reduce(0, +)
        }.min()!
    answer += n * Int(passwd.joined().dropLast())!
}
print(answer)