d20p2
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186
day20/d20p2.swift
Normal file
186
day20/d20p2.swift
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import Foundation
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struct Coord : Hashable, CustomStringConvertible {
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let (x, y): (Int, Int)
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var description: String { return "(\(x), \(y))" }
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}
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struct Queue<T> {
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var arr: [T?]
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var front: Int = 0
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var back: Int = 0
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init(size: Int) {
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arr = Array(repeating: nil, count: size)
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}
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mutating func push(_ element: T) {
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arr[back] = element
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back += 1
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}
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mutating func pop() -> T? {
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if front < back {
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front += 1
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return arr[front-1]
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}
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return nil
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}
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}
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struct Maze : CustomStringConvertible {
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let (w, h): (Int, Int)
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let walls: Set<Coord>
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let (start, end): (Coord, Coord)
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let cheatMax: Int
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var description: String {
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var s = Array(repeating: Array(repeating: " ", count: w), count: h)
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walls.forEach { wall in
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s[wall.y][wall.x] = "██"
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}
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path.forEach { cell, cost in
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s[cell.y][cell.x] = String(format: "%2d", cost%100)
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}
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let hdr = " " + (0..<w).map { " \($0 % 10)" }.joined() + "\n"
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return hdr +
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s.enumerated().map { i, c in
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String(format: "%2d ", i) + c.joined() + "\n"
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}.joined() + "\(start), \(end)"
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}
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var path: [Coord: Int] {
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var cost: [Coord: Int] = [start: 0]
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var cell = start
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var prev = start
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var currentCost = 0
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while cell != end {
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let next = neighbors(of: cell)
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.filter(isPath)
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.filter { $0 != prev }[0]
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currentCost += 1
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cost[next] = currentCost
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prev = cell
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cell = next
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}
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return cost
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}
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func valid(_ cell: Coord) -> Bool {
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return cell.x >= 0 && cell.x < w && cell.y >= 0 && cell.y < h
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}
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func isPath(_ cell: Coord) -> Bool {
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return !walls.contains(cell)
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}
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func isWall(_ cell: Coord) -> Bool {
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return walls.contains(cell)
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}
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func neighbors(of cell: Coord) -> [Coord] {
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return [(-1, 0), (1, 0), (0, -1), (0, 1)]
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.map { Coord(x: cell.x + $0, y: cell.y + $1) }.filter(valid)
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}
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/*
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func cheats(from entryCell: Coord) -> [Coord: Int] {
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var q = Queue<(Coord, Int)>(size: cheatMax*cheatMax*2*2)
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q.push((entryCell, 0))
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var seen: Set<Coord> = [entryCell]
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var jumps: [Coord: Int] = [:]
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while let (cell, dist) = q.pop() {
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neighbors(of: cell).filter { !seen.contains($0) }.forEach { nb in
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seen.insert(nb)
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if isPath(nb) {
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if dist + 1 <= cheatMax {
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//print("\(cell) -> \(nb) . \(dist + 1)")
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jumps[nb] = min(jumps[nb] ?? Int.max, dist + 1)
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}
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} else if dist < cheatMax {
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//print("\(cell) -> \(nb) # \(dist + 1)")
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q.push((nb, dist + 1))
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}
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}
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}
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return jumps
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}
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*/
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func cheats(from entry: Coord) -> [Coord: Int] {
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let jumpList: [(Int, Int)] = (2...cheatMax).flatMap { dist in
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(0..<dist).flatMap { d in
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let asdf: [(Int, Int)] = [
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(d, dist-d), (dist-d, -d), (-d, d-dist), (d-dist, d)
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]
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return asdf
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}
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}
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let jumpCoords: [Coord] = jumpList
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.map { dx, dy in Coord(x: entry.x + dx, y: entry.y + dy) }
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.filter(valid).filter(isPath)
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var res: [Coord: Int] = [:]
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jumpCoords.forEach { end in
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res[end] = abs(end.x - entry.x) + abs(end.y - entry.y)
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}
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return res
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}
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func cheats() -> [(Coord, Coord, Int, Int)] {
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var cost: [Coord: Int] = [start: 0]
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var jumps: [(Coord, Coord, Int)] = []
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var cell = start
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var prev = start
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var currentCost = 0
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while cell != end {
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// list potential cheats from current cell
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let newCheats = cheats(from: cell)
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.filter { dest, _ in !cost.keys.contains(dest) }
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.map { dest, dist in (cell, dest, dist) }
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jumps.append(contentsOf: newCheats)
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// add cost to table
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let next = neighbors(of: cell)
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.filter(isPath)
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.filter { $0 != prev }[0]
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currentCost += 1
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cost[next] = currentCost
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prev = cell
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cell = next
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//print("looking at \(cell) \(cost[cell]!)")
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}
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return jumps.map { from, to, dist in (from, to, cost[to]! - cost[from]! - dist, dist) }
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}
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}
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func readInput(_ filePath: String, _ cheatMax: Int) throws -> Maze {
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let content = try String(contentsOfFile: filePath, encoding: .ascii)
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let lines = content.split(separator: "\n")
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let (w, h) = (lines[0].count, lines.count)
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var walls: Set<Coord> = []
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var (start, end) = (Coord(x: 0, y: 0), Coord(x: w-1, y: h-1))
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lines.enumerated().forEach { i, line in
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line.enumerated().forEach { j, cell in
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let coord = Coord(x: j, y: i)
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if cell == "#" {
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walls.insert(coord)
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} else if cell == "S" {
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start = coord
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} else if cell == "E" {
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end = coord
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}
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}
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}
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return Maze(
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w: w, h: h, walls: walls, start: start, end: end, cheatMax: cheatMax
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)
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}
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let maze = try readInput(CommandLine.arguments[1], Int(CommandLine.arguments[2])!)
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print(maze)
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// print(maze.cheats(from: maze.start))
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let cheats = maze.cheats().filter { _, _, saving, _ in saving > 0 }
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let hist = cheats.reduce(into: [:]) { n, t in n[t.2, default: 0] += 1 }
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hist.keys.sorted().forEach { print("\(hist[$0]!) - \($0)") }
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print(cheats.filter { $0.2 >= 100 }.count)
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/*
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cheats
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.filter { _, _, saving, _ in saving == 72 }
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.forEach { from, to, save, dist in
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print("\(path[from]!) -> \(path[to]!) = \(dist)(\(save))")
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}
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print()
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*/
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