d05

day05/d05p1.swift

@@ -0,0 +1,40 @@
+import Foundation
+
+func readInput(_ filePath: String) throws -> ([Int: Set<Int>], [[Int]]) {
+    let content = try String(contentsOfFile: filePath, encoding: .ascii)
+    var rules: [Int: Set<Int>] = [:]
+    var pages: [[Int]] = []
+    var readingRules = true
+    for l in content.split(separator: "\n", omittingEmptySubsequences: false) {
+        if l == "" {
+            readingRules = false
+            continue
+        }
+        if readingRules {
+            let rule = l.split(separator: "|").map { Int($0)! }
+            let (before, after) = (rule[0], rule[1])
+            let current = rules[before, default: []]
+            rules[before] = current.union([after])
+        } else {
+            pages.append(l.split(separator: ",").map { Int($0)! })
+        }
+    }
+    return (rules, pages)
+}
+
+func goodPages(_ pages: [Int], against rules: [Int: Set<Int>]) -> Bool {
+    var seen: Set<Int> = []
+    for page in pages {
+        if !rules[page, default: []].isDisjoint(with: seen) {
+            return false
+        }
+        seen.insert(page)
+    }
+    return true
+}
+
+let (rules, manuals) = try readInput(CommandLine.arguments[1])
+let answer = manuals
+    .filter { goodPages($0, against: rules) }
+    .map { $0[$0.count/2] }.reduce(0, +)
+print(answer)