Find neighbours

Author: mnvr

21.swift

@@ -3,7 +3,10 @@
 // Part 1: Do a BFS to find all reachable nodes within 64 steps.
 
 typealias Map = [[Character]]
-typealias Coordinate = (x: Int, y: Int)
+
+struct Coordinate: Hashable {
+    let x, y: Int
+}
 
 struct Grid {
     let map: Map
@@ -13,20 +16,34 @@ struct Grid {
     init(map: Map) {
         self.map = map
         self.start = Grid.findStart(map)
-        self.max = (map[0].count, map.count)
+        self.max = Coordinate(x: map[0].count, y: map.count)
     }
 
     static func findStart(_ map: Map) -> Coordinate {
         for (y, row) in map.enumerated() {
             for (x, c) in row.enumerated() {
-                if c == "S" { return (x, y) }
+                if c == "S" { return Coordinate(x: x, y: y) }
             }
         }
         fatalError()
     }
 
+    func at(_ c: Coordinate) -> Character {
+        map[c.y][c.x]
+    }
+
     func neighbours(of c: Coordinate) -> [Coordinate] {
-        return []
+        potentialNeighbours(c).filter { inBounds($0) && at($0) != "#" }
+    }
+
+    func inBounds(_ c: Coordinate) -> Bool {
+        c.x >= 0 && c.x <= max.x &&
+        c.y >= 0 && c.y <= max.y
+    }
+
+    func potentialNeighbours(_ c: Coordinate) -> [Coordinate] {
+        [(c.x - 1, c.y), (c.x + 1, c.y), (c.x, c.y - 1), (c.x, c.y + 1)]
+            .map { Coordinate(x: $0, y: $1) }
     }
 }
 
@@ -44,9 +61,10 @@ func readInput() -> Grid {
     return Grid(map: map)
 }
 
-// func bfs(_ map: Map) -> Int {
-//     var visited: Set
-// }
+func bfs(_ map: Map) -> Int {
+    var visited: Set<Coordinate> = Set()
+    return 0
+}
 
 let grid = readInput()
 print(grid)