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2020/day7/main.swift

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+import Foundation
+
+let input = loadData(day: 7)
+
+
+let scanner = Scanner(string: input)
+
+struct Rule {
+    var count: Int
+    var color: String
+}
+
+extension Scanner {
+    func scanRule() -> Rule? {
+        guard let count = scanInt(),
+              let color = scanUpToString(count == 1 ? " bag" : " bags"),
+              scanString(count == 1 ? "bag" : "bags") != nil
+              else { return nil }
+        return Rule(count: count, color: color)
+    }
+
+    func scanRuleSet() -> (String, [Rule])? {
+        guard
+            let color = scanUpToString(" bags contain"),
+            scanString("bags contain") != nil else { return nil }
+        if scanString("no other bags.") != nil {
+            return (color, [])
+        }
+
+        var rules: [Rule] = []
+        repeat {
+            guard let rule = scanRule() else { return nil }
+            rules.append(rule)
+        } while scanString(",") != nil
+
+        guard scanString(".") != nil else { return nil }
+
+        return (color, rules)
+    }
+
+    func scanAllRules() -> [String: [Rule]]? {
+        var result: [String: [Rule]] = [:]
+        while !isAtEnd {
+            guard let (color, rules) = scanRuleSet() else { return nil }
+            result[color] = rules
+        }
+        return result
+    }
+}
+
+guard let rules = scanner.scanAllRules() else { fatalError() }
+//print(rules)
+
+func findPath(rules: [String: [Rule]], from: String, to: String) -> Bool {
+    guard let from = rules[from] else { return false }
+    if from.contains(where: { $0.color == to }) {
+        return true
+    }
+
+    return from.contains(where: { findPath(rules: rules, from: $0.color, to: to) })
+}
+
+let count = rules.lazy.filter { findPath(rules: rules, from: $0.key, to: "shiny gold") }.count
+
+print("count", count)
+
+func bagsInside(rules: [String: [Rule]], color: String) -> Int {
+    guard let from = rules[color] else { return 0 }
+    return from.reduce(0) { accum, bag in
+        accum + bag.count + bag.count * bagsInside(rules: rules, color: bag.color)
+    }
+}
+
+print("total bags", bagsInside(rules: rules, color: "shiny gold"))