import Foundation

struct Coord : Hashable, CustomStringConvertible {
    let x: Int
    let y: Int
    var description: String { return "(\(x), \(y))" }
    func neighbors() -> [Coord] {
        return [
            Coord(x: x-1, y: y), Coord(x: x+1, y: y),
            Coord(x: x, y: y-1), Coord(x: x, y: y+1)
        ]
    }
}

func readInput(_ filePath: String) throws -> ([Int:Set<Coord>], Int, Int) {
    let content = try String(contentsOfFile: filePath, encoding: .ascii)
    let lines = content.split(separator: "\n").map(Array.init)
    let map = lines.map { $0.map(String.init).map { Int($0)! } }
    var topo: [Int:Set<Coord>] = [:]
    map.enumerated().forEach { i, row in
        row.enumerated().forEach { j, h in
            topo[h] = (topo[h] ?? []).union([Coord(x: i, y: j)])
        }
    }
    return (topo, lines.count, lines[0].count)
}

let (topo, height, width) = try readInput(CommandLine.arguments[1])
topo.forEach { k, v in print("\(k): \(v)") }

var currentLayer: [Coord:Int] = Dictionary(
    uniqueKeysWithValues: topo[0]!.map { coord in (coord, 1) }
)
print("\n0: \(currentLayer)")
for alt in 1...9 {
    var nextLayer: [Coord:Int] = [:]
    for (from, score) in currentLayer {
        from.neighbors()
            .filter { c in c.x >= 0 && c.y >= 0 && c.x < height && c.y < width }
            .filter { c in topo[alt]!.contains(c) }
            .forEach { c in nextLayer[c] = (nextLayer[c] ?? 0) + score }
    }
    currentLayer = nextLayer
    print("\(alt): \(currentLayer)")
}
print(currentLayer.values.reduce(0) { s, score in s + score })