d04

day04/d04p1.swift

@@ -0,0 +1,51 @@
+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 XMAS: (Character, Character, Character, Character) = ("X", "M", "A", "S")
+
+func dE(_ map: [[Character]], _ i: Int, _ j: Int) -> Bool {
+    return j < map[i].count - 3
+        && (map[i][j], map[i][j+1], map[i][j+2], map[i][j+3]) == XMAS
+}
+func dW(_ map: [[Character]], _ i: Int, _ j: Int) -> Bool {
+    return j >= 3
+        && (map[i][j], map[i][j-1], map[i][j-2], map[i][j-3]) == XMAS
+}
+func dS(_ map: [[Character]], _ i: Int, _ j: Int) -> Bool {
+    return i < map.count - 3
+        && (map[i][j], map[i+1][j], map[i+2][j], map[i+3][j]) == XMAS
+}
+func dN(_ map: [[Character]], _ i: Int, _ j: Int) -> Bool {
+    return i >= 3
+        && (map[i][j], map[i-1][j], map[i-2][j], map[i-3][j]) == XMAS
+}
+func dNW(_ map: [[Character]], _ i: Int, _ j: Int) -> Bool {
+    return i >= 3 && j >= 3
+        && (map[i][j], map[i-1][j-1], map[i-2][j-2], map[i-3][j-3]) == XMAS
+}
+func dSE(_ map: [[Character]], _ i: Int, _ j: Int) -> Bool {
+    return i < map.count - 3 && j < map[i].count - 3
+        && (map[i][j], map[i+1][j+1], map[i+2][j+2], map[i+3][j+3]) == XMAS
+}
+func dNE(_ map: [[Character]], _ i: Int, _ j: Int) -> Bool {
+    return i >= 3 && j < map[i].count - 3
+        && (map[i][j], map[i-1][j+1], map[i-2][j+2], map[i-3][j+3]) == XMAS
+}
+func dSW(_ map: [[Character]], _ i: Int, _ j: Int) -> Bool {
+    return i < map.count - 3 && j >= 3
+        && (map[i][j], map[i+1][j-1], map[i+2][j-2], map[i+3][j-3]) == XMAS
+}
+
+func xmasCount(_ map: [[Character]], _ i: Int, _ j: Int) -> Int {
+    let funcs = [dE, dW, dS, dN, dNW, dSE, dNE, dSW]
+    return funcs.reduce(0, { sum, f in f(map, i, j) ? sum+1 : sum })
+}
+
+let input = try readInput(CommandLine.arguments[1])
+let answer = (0..<input.count).reduce(0, { n, i in n +
+    (0..<input[i].count).reduce(0, { n, j in n + xmasCount(input, i, j) }) })
+print(answer)