d20p2

day20/d20p1.swift

@@ -20,21 +20,19 @@ struct Maze : CustomStringConvertible {
         }
         return s.map { $0.joined() + "\n" }.joined() + "\(start), \(end)"
     }
-    let adjacents = [(-1, 0), (1, 0), (0, -1), (0, 1)]
 
     func valid(_ cell: Coord) -> Bool {
         return cell.x >= 0 && cell.x < w && cell.y >= 0 && cell.y < h &&
             !walls.contains(cell)
     }
 
-    func neighbor(of cell: Coord, isNot excluded: Coord) -> Coord {
-        return adjacents
+    func neighbors(of cell: Coord) -> [Coord] {
+        return [(-1, 0), (1, 0), (0, -1), (0, 1)]
             .map { dx, dy in Coord(x: cell.x + dx, y: cell.y + dy) }
-            .filter { newCell in valid(newCell) && newCell != excluded }[0]
     }
 
     func cheats(of cell: Coord) -> [Coord] {
-        return adjacents
+        return [(-1, 0), (1, 0), (0, -1), (0, 1)]
             .map { dx, dy in Coord(x: cell.x + dx*2, y: cell.y + dy*2) }
             .filter(valid)
     }
@@ -43,18 +41,18 @@ struct Maze : CustomStringConvertible {
         var cost: [Coord: Int] = [start: 0]
         var jumps: [(Coord, Coord)] = []
         var cell = start
-        var prevCell = start
+        var prev = start
         var currentCost = 0
         while cell != end {
             // list potential cheats from current cell
             let newCheats = cheats(of: cell).filter { !cost.keys.contains($0) }
             jumps.append(contentsOf: newCheats.map { dest in (cell, dest)} )
             // add cost to table
-            let nextCell = neighbor(of: cell, isNot: prevCell)
+            let next = neighbors(of: cell).filter(valid).filter { $0 != prev }[0]
             currentCost += 1
-            cost[nextCell] = currentCost 
-            prevCell = cell
-            cell = nextCell
+            cost[next] = currentCost
+            prev = cell
+            cell = next
         }
         return jumps.map { from, to in cost[to]! - cost[from]! - 2 }
     }
@@ -84,6 +82,7 @@ func readInput(_ filePath: String) throws -> Maze {
 let maze = try readInput(CommandLine.arguments[1])
 print(maze)
 let cheats = maze.cheats()
-print(cheats.reduce(into: [:]) { counts, t in counts[t, default: 0] += 1 })
+let hist = cheats.reduce(into: [:]) { counts, t in counts[t, default: 0] += 1 }
+hist.keys.sorted().forEach { print("\($0) -> \(hist[$0]!)") }
 print(cheats.filter { $0 >= 100 }.count)