d10

day10/d10p1.swift

@@ -0,0 +1,49 @@
+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 valid(xLimit: Int, yLimit: Int) -> Bool {
+        return x >= 0 && y >= 0 && x < xLimit && y < yLimit
+    }
+}
+
+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])
+var answer: Int = 0
+//topo.forEach { k, v in print("\(k): \(v)") }
+
+for start in topo[0]! {
+    var froms: Set<Coord> = [start]
+    for altitude in 1...9 {
+        var tos: Set<Coord> = []
+        for from in froms {
+            from.neighbors()
+                .filter { c in c.valid(xLimit: height, yLimit: width) }
+                .filter { c in topo[altitude]!.contains(c) }
+                .forEach { c in tos.insert(c) }
+        }
+        froms = tos
+    }
+    answer += froms.count
+}
+print(answer)