d12

day12/d12p2.swift

@@ -0,0 +1,93 @@
+import Foundation
+
+struct Plot : Hashable, CustomStringConvertible {
+    let x: Int
+    let y: Int
+    var description: String { return "Plot(\(x), \(y))" }
+}
+
+struct Map : CustomStringConvertible {
+    let map: [[Character]]
+    let (w, h): (Int, Int)
+    var visited: [[Bool]]
+
+    var description: String {
+        var ret: String = "\(w)x\(h):\n"
+        for i in 0..<map.count {
+            for j in 0..<map[i].count {
+                ret.append(map[i][j])
+                ret.append(visited[i][j] ? "." : " ")
+            }
+            ret.append("\n")
+        }
+        return ret
+    }
+    init(_ map: [[Character]]) {
+        self.map = map
+        self.visited = map.map { $0.map { _ in false } }
+        self.h = map.count
+        self.w = map[0].count
+    }
+
+    // visits a plot; returns its perimeter contribution & unvisited neighbors
+    mutating func visit(_ plot: Plot) -> (Int, [Plot]) {
+        let (x, y) = (plot.x, plot.y)
+        visited[x][y] = true
+        let all_nbs = [(x-1, y), (x+1, y), (x, y-1), (x, y+1)]
+        let peri = all_nbs.filter { i, j in
+            i < 0 || j < 0 || i >= h || j >= w || map[i][j] != map[x][y]
+        }.count
+        let nbs = all_nbs.filter { i, j in
+            i >= 0 && j >= 0 && i < h && j < w &&
+            map[i][j] == map[x][y] &&
+            !visited[i][j]
+        }.map { i, j in Plot(x: i, y: j) }
+        return (peri, nbs)
+    }
+
+    mutating func visitAll(from plot: Plot) -> Int {
+        var q: Set<Plot> = [plot]
+        var region: Set<Plot> = []
+        var peri = 0
+        var area = 0
+        while !q.isEmpty {
+            let currentPlot = q.removeFirst()
+            let (newPeri, newNBs) = visit(currentPlot)
+            region.insert(currentPlot)
+            peri += newPeri
+            area += 1
+            q.formUnion(newNBs)
+        }
+        for i in -1..<h {
+            for j in -1..<w {
+                let ul = region.contains(Plot(x: i, y: j))
+                let ur = region.contains(Plot(x: i, y: j+1))
+                let ll = region.contains(Plot(x: i+1, y: j))
+                let lr = region.contains(Plot(x: i+1, y: j+1))
+                if (ul && ur && !ll && !lr) || (ul && !ur && ll && !lr) ||
+                   (!ul && ur && !ll && lr) || (!ul && !ur && ll && lr) {
+                    peri -= 1
+                }
+            }
+        }
+        print("\(map[plot.x][plot.y]): \(area)x\(peri)")
+        return peri * area
+    }
+}
+
+func readInput(_ filePath: String) throws -> Map {
+    let content = try String(contentsOfFile: filePath, encoding: .ascii)
+    return Map(content.split(separator: "\n").map(Array.init))
+}
+
+var map = try readInput(CommandLine.arguments[1])
+print(map)
+var answer = 0
+for i in 0..<map.h {
+    for j in 0..<map.w {
+        if !map.visited[i][j] {
+            answer += map.visitAll(from: Plot(x: i, y: j))
+        }
+    }
+}
+print(answer)