Base62

Base62.swift

import Foundation

let base62Alphabet: [Character] = [
  "0", "1", "2", "3", "4", "5", "6", "7", "8", "9",
  "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M",
  "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z",
  "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m",
  "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z",
]

public func encode(integer: UInt64) -> String {
  return encode(integer: integer, alphabet: base62Alphabet)
}

func encode(integer: UInt64, alphabet: [Character]) -> String {
  let base = UInt64(alphabet.count)
  
  if integer < base {
    return String(alphabet[Int(integer)])
  }
  return encode(integer: integer / base, alphabet: alphabet) + String(alphabet[Int(integer % base)])
}

func readDay1(_ string: String) -> [Double] {
  var buffer = ""
  var values = [Double]()
  
  func decode(_ string: String) -> Double {
    let base = Double(base62Alphabet.count)
    var output: UInt64 = 0
    
    for (i, c) in string.enumerated() {
      guard let index = base62Alphabet.index(of: c)
        else { continue }
      let place = UInt64(pow(base, Double(i)))
      output += UInt64(index) * place
    }
    
    return Double(output)
  }
  
  for c in string.reversed() {
    switch c {
    case "-":
      values.append(decode(buffer) * -1)
      buffer.removeAll()
    case "+":
      values.append(decode(buffer))
      buffer.removeAll()
    default:
      buffer.append(c)
    }
  }
  
  return values.reversed()
}

func readDay2(_ string: String) -> [Double] {
  var idx = string.endIndex
  var values = [Double]()
  
  func decode(_ substring: Substring) -> Double {
    let base = UInt64(base62Alphabet.count)
    var output: UInt64 = 0
    
    for c in substring {
      guard let index = base62Alphabet.index(of: c)
        else { continue }
      output = base * output + UInt64(index)
    }
    
    return Double(output)
  }
  
  for (c, i) in zip(string.reversed(), string.indices.reversed()) {
    switch c {
    case "-":
      values.append(decode(string[i..<idx]) * -1)
      idx = i
    case "+":
      values.append(decode(string[i..<idx]))
      idx = i
    default:
      continue
    }
  }
  
  return values.reversed()
}

func readDay3(_ string: String) -> [Double] {
  var values = [Double]()
  let base = Double(base62Alphabet.count)
  var output: UInt64 = 0
  var i = 0
  for c in string.reversed() {
    if let index = base62Alphabet.index(of: c) {
      let place = UInt64(pow(base, Double(i)))
      output += UInt64(index) * place
      i += 1
    } else {
      values.append(Double(output) * (c == "-" ? -1 : 1))
      output = 0
      i = 0
    }
  }
  return values.reversed()
}

let day1 = "+w-e-1h-24-2G-2S-2O-M+4v+B3+Fb+Ia+KD+KZ+Jy+Ha+CB+78+52+47+2u+1c+U-M"

let temp1 = readDay1(day1).map { $0 / 100 }
let temp2 = readDay2(day1).map { $0 / 100 }
let temp3 = readDay3(day1).map { $0 / 100 }