AdventOfCode.com 2016/Day 5 Solution

Day5_NSViewController.swift

//
//  ViewController.swift
//  AdventOfCodeMac
//
//  Created by Scott Atkinson on 12/17/16.
//  Copyright © 2016 Fathouse Software. All rights reserved.
//

import Cocoa

class ViewController: NSViewController {
    
    //: ## Input Processing
    let testInput = "cxdnnyjw"
    
    @IBAction func go(_ sender: Any) {
        
        //: ## Solution Execution
        
        //: ### Part 1
        var doorCode = ""
        var doorCodeArray: [String?] = [nil, nil, nil, nil, nil, nil, nil, nil]
        var hashSeed = 0
        var foundChars = 0
        
        print("Starting: \(Date())")
        while (doorCode.characters.count < 8) || (foundChars < 8) {
            let seed = "\(testInput)\(hashSeed)"
            let md5 = MD5(seed)
            
            if hasLeadingDigits(hash: md5) {
                
                // Part 1
                if doorCode.characters.count < 8 {
                    doorCode.append(character(at: 5, inHash: md5))
                }
                
                // Part 2
                if let position = Int(character(at: 5, inHash: md5)), position < doorCodeArray.count {
                    if doorCodeArray[position] == nil {
                        doorCodeArray[position] = character(at: 6, inHash: md5)
                        foundChars += 1
                    }
                }
            }
            hashSeed += 1
        }
        
        print("Part 1 Answer: \(doorCode)\n")
        
        //: ### Part 2
        print("Part 2 Answer: \(doorCodeArray.flatMap({$0}).joined())")
        
        print("Done: \(Date())")
    }
}

func string(fromFile name:String, fileExtension:String) -> String? {
    
    if let filePath = Bundle.main.path(forResource:name, ofType:fileExtension) {
        if let inputData = FileManager.default.contents(atPath: filePath) {
            return String(data: inputData, encoding: .utf8)
        }
    }
    return nil
}

//: ## Solution Objects & Functions
func MD5(_ string: String) -> [UInt8] {
    let context = UnsafeMutablePointer<CC_MD5_CTX>.allocate(capacity: 1)
    var digest = Array<UInt8>(repeating:0, count:Int(CC_MD5_DIGEST_LENGTH))
    CC_MD5_Init(context)
    CC_MD5_Update(context, string, CC_LONG(string.lengthOfBytes(using: String.Encoding.utf8)))
    CC_MD5_Final(&digest, context)
    context.deallocate(capacity: 1)
    return digest
}

func hasLeadingDigits(hash:[UInt8]) -> Bool {
    guard hash.count >= 3 else { return false }
    
    return hash[0] == 0
        && hash[1] == 0
        && hash[2] < 0x10
}


// Part 2 Solution
func character(at position:Int, inHash:[UInt8]) -> String {
    guard position < inHash.count * 2 else { return "" }
    
    let element = position/2
    let characterPos = position%2
    
    if characterPos == 0 {
        return String(String(format:"%02x", inHash[element]).characters.first!)
    } else {
        return String(String(format:"%02x", inHash[element]).characters.last!)
    }
}

Had to use Mac app for this one so I could use CommonCrypto and more speed