Solution_2018_05.swift

import Foundation

struct Solution_2018_05: Solution {
    var input: Input
    func run() throws {
        let polymer = try input.get()
        //let polymer = input[input.startIndex...input.index(input.startIndex, offsetBy: 20)]

        func shouldAnnihilate(_ a: Character, _ b: Character) -> Bool {
            return a.lowercased() == b.lowercased()
                && ((a.isLowercase && b.isUppercase) || (a.isUppercase && b.isLowercase))
        }

        let result: [Character] = polymer.reduce(into: []) { acc, c in
            if let top = acc.last, shouldAnnihilate(c, top) {
                acc.removeLast()
            } else {
                acc.append(c)
            }
        }
        let part1 = result.count
        print(part1)

        let map: [Character:[Character]] = polymer.reduce(into: [Character: [Character]]()) { acc, c in
            "abcdefghijklmnopqrstuvwxyz".forEach { k in
                guard String(k) != c.lowercased() else {
                    return
                }
                if let top = acc[k]?.last, shouldAnnihilate(c, top) {
                    acc[k]!.removeLast()
                } else {
                    acc[k, default: []].append(c)
                }
            }
        }
        let part2 = map.values.map({ $0.count }).min()
        print(part2!)

        // ------- Test -------

        assert(part1 == 11298, "WA")
        assert(part2 == 5148, "WA")
    }
}