Advent of Code Day 7

Day7.swift

//: Playground - noun: a place where people can play
import Foundation

let inputString: String = """
pbga (66)
xhth (57)
ebii (61)
havc (66)
ktlj (57)
fwft (72) -> ktlj, cntj, xhth
qoyq (66)
padx (45) -> pbga, havc, qoyq
tknk (41) -> ugml, padx, fwft
jptl (61)
ugml (68) -> gyxo, ebii, jptl
gyxo (61)
cntj (57)
"""

var lines = inputString.split(separator: "\n")

let outerpattern = "([a-z]+) \\(([0-9]+)\\)(?: -> ((?:[a-z]+(?:, )?)+))?"
let re = try! NSRegularExpression(pattern: outerpattern)

struct Program {
    var name : String
    var children : [String]
    var weight : Int
    var parent : String?
}

var programs : [String : Program] = [:];
var relationships : [String: [String]] = [:];

for line in lines {
    let range = NSMakeRange(0, line.count)
    let matches = re.matches(in: String(line), options: NSRegularExpression.MatchingOptions(), range: range)
    
    for match in matches {
        var programName : String = ""
        var weight : Int = 0
        var children : String = ""
        
        for y in 0..<match.numberOfRanges {

            if match.range(at: y).lowerBound > line.count {
                continue;
            }
            let matchValue = ((line as NSString).substring(with: match.range(at: y)))
            switch y {
                case 1:
                    programName = matchValue
                case 2:
                    if let weightInt = Int(matchValue) {
                        weight = weightInt
                    } else {
                        weight = 0
                    }
                case 3:
                    children = matchValue
                default:
                    continue
            }
        }
        let childrenArray = children.split(separator: ",").map({
            $0.trimmingCharacters(in: .whitespaces)
        })
        programs[programName] = Program(name: programName, children: childrenArray, weight: weight, parent: nil)
    }
}
for (name, parent) in programs {
    for child in parent.children {
        if var childProgram = programs[child] {
            childProgram.parent = parent.name
            programs[child] = childProgram
        }
    }
}
print (
    programs.filter ({ (name, program) -> Bool in
        program.parent == nil
    }).map({(name, program) -> String in name})
)