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)

day05/d05p2.swift

@@ -0,0 +1,66 @@
+import Foundation
+
+func readInput(_ filePath: String) throws -> ([(Int, Int)], [[Int]]) {
+    let content = try String(contentsOfFile: filePath, encoding: .ascii)
+    var rules: [(Int, 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)! }
+            rules.append((rule[0], rule[1]))
+        } else {
+            pages.append(l.split(separator: ",").map { Int($0)! })
+        }
+    }
+    return (rules, pages)
+}
+
+func rulesMap(_ rulePairs: [(Int, Int)]) -> [Int: Set<Int>] {
+    var rules: [Int: Set<Int>] = [:]
+    for (from, to) in rulePairs {
+        let current = rules[from, default: []]
+        rules[from] = current.union([to])
+    }
+    return rules
+}
+
+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
+}
+
+func reorder(_ originalPages: [Int], conformTo rules: [(Int, Int)]) -> [Int] {
+    let pages = Set(originalPages)
+    var graph = rulesMap(
+        rules.filter { from, to in pages.contains(from) && pages.contains(to) }
+    )
+
+    // Topological sort
+    var sorted: [Int] = []
+    while graph.count > 0 {
+        let outNodes: Set<Int> = graph.reduce([], { s, i in s.union(i.value) })
+        let inNodes = Set(graph.compactMap { !outNodes.contains($0.key) ? $0.key : nil })
+        graph = graph.filter { !inNodes.contains($0.key) }
+        sorted += inNodes
+    }
+    return sorted
+}
+
+let (rules, manuals) = try readInput(CommandLine.arguments[1])
+let answer = manuals
+    .filter { !goodPages($0, against: rulesMap(rules)) }
+    .map { reorder($0, conformTo: rules) }
+    .map { $0[$0.count/2] }
+    .reduce(0, +)
+print(answer)

day05/test.txt

@@ -0,0 +1,28 @@
+47|53
+97|13
+97|61
+97|47
+75|29
+61|13
+75|53
+29|13
+97|29
+53|29
+61|53
+97|53
+61|29
+47|13
+75|47
+97|75
+47|61
+75|61
+47|29
+75|13
+53|13
+
+75,47,61,53,29
+97,61,53,29,13
+75,29,13
+75,97,47,61,53
+61,13,29
+97,13,75,29,47