Initial commit

day11/main.swift

@@ -0,0 +1,116 @@
+import Foundation
+
+let input = loadData(day: 11)
+
+enum Spot: Equatable {
+    case empty
+    case occupied
+    case floor
+}
+typealias Map = [[Spot]]
+
+var map: Map = []
+
+input.enumerateLines { (line, _) in
+    map.append(line.map {
+        switch $0 {
+        case ".": return .floor
+        case "#": return .occupied
+        case "L": return .empty
+        default: fatalError("Invalid input")
+        }
+    })
+}
+
+
+let adjacents = [
+    (-1, -1),
+    (0, -1),
+    (1, -1),
+    (-1, 0),
+    (1, 0),
+    (-1, 1),
+    (0, 1),
+    (1, 1)
+]
+
+/*
+ func step(map: Map) -> Map {
+     var result = map
+     let width = map[0].count
+
+     for i in 0..<map.count {
+         for j in 0..<width where map[i][j] != .floor {
+             let occupieds = adjacents.reduce(0) { count, offset in
+                 let (x, y) = (offset.0 + j, offset.1 + i)
+                 guard 0..<map.count ~= y, 0..<width ~= x else { return count }
+                 return count + (map[y][x] == .occupied ? 1 : 0)
+             }
+             switch (map[i][j], occupieds) {
+             case (.empty, 0): result[i][j] = .occupied
+             case (.occupied, let n) where n >= 4: result[i][j] = .empty
+             default: break
+             }
+         }
+     }
+
+     return result
+ }
+
+ */
+
+func occupiedInDirection(at pos: (Int, Int), map: Map, direction: (Int, Int)) -> Int {
+    var pos = pos
+
+    let yRange = 0..<map.count
+    let xRange = 0..<map[0].count
+
+    while true {
+        var (i, j) = pos
+        i+=direction.1
+        j += direction.0
+        pos = (i, j)
+
+        guard yRange ~=  pos.0, xRange ~= pos.1 else { break }
+        
+        let state = map[i][j]
+        switch state {
+        case .floor: break
+        case .occupied: return 1
+        case .empty: return 0
+        }
+    }
+    return 0
+}
+
+func step(map: Map) -> Map {
+    var result = map
+    let width = map[0].count
+
+    for i in 0..<map.count {
+        for j in 0..<width where map[i][j] != .floor {
+            let occupieds = adjacents.reduce(0) { count, offset in
+                count + occupiedInDirection(at: (i, j), map: map, direction: offset)
+            }
+            switch (map[i][j], occupieds) {
+            case (.empty, 0): result[i][j] = .occupied
+            case (.occupied, let n) where n >= 5: result[i][j] = .empty
+            default: break
+            }
+        }
+    }
+
+    return result
+}
+
+
+while true {
+    let next = step(map: map)
+    if next == map {
+        break
+    }
+    map = next
+}
+
+let totalOccupieds = map.lazy.flatMap { $0 }.filter { $0 == .occupied }.count
+print(totalOccupieds)