67 lines
2.0 KiB
Swift
67 lines
2.0 KiB
Swift
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 = graph.filter { !outNodes.contains($0.key) }.keys
|
|
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)
|