d04

day04/d04p2.swift

@@ -0,0 +1,21 @@
+import Foundation
+
+func readInput(_ filePath: String) throws -> [[Character]] {
+    let content = try String(contentsOfFile: filePath, encoding: .ascii)
+    return content.split(separator: "\n").map(Array.init)
+}
+
+let MAS: (Character, Character, Character) = ("M", "A", "S")
+
+func dX(_ map: [[Character]], _ i: Int, _ j: Int) -> Bool {
+    return ((map[i-1][j-1], map[i][j], map[i+1][j+1]) == MAS
+            || (map[i+1][j+1], map[i][j], map[i-1][j-1]) == MAS)
+        && ((map[i-1][j+1], map[i][j], map[i+1][j-1]) == MAS
+            || (map[i+1][j-1], map[i][j], map[i-1][j+1]) == MAS)
+}
+
+let input = try readInput(CommandLine.arguments[1])
+let answer = (1..<input.count-1).reduce(0, { n, i in
+    n + (1..<input[i].count-1).reduce(0, { n, j in dX(input, i, j) ? n+1 : n })
+})
+print(answer)