AdventOfCode.com 2016 Day 2 Solution (http://adventofcode.com/2016/day/2) (Part 2)

Day2Part2.playground.swift

import Foundation

enum Instruction:String {
    case up = "U"
    case down = "D"
    case left = "L"
    case right = "R"
}

extension Int {
    func nextDigit(withInstruction instruction:Instruction, keypad:[[Int?]]) -> Int {
    
        var rowIdx = -1
        var colIdx = -1
        
        // Determine location of digit on keypad
        rowLoop: for row in keypad {
            rowIdx+=1
            colIdx = -1
            for digit in row {
                colIdx+=1
                if digit == self { break rowLoop }
            }
        }
        
        // Move in the correct direction on the keypad
        switch instruction {
        case .up:
            rowIdx -= 1
        case .down:
            rowIdx += 1
        case .left:
            colIdx -= 1
        case .right:
            colIdx += 1
        }
 
        // Moved off the edge of the keypad, or self is not on the keypad
        guard rowIdx < keypad.count, rowIdx >= 0,
            colIdx < keypad.first!.count, colIdx >= 0 else {
                return self
        }
        
        return keypad[rowIdx][colIdx] ?? self
    }
}

// Day 2:
let testInput = "ULL\nRRDDD\nLURDL\nUUUUD"
let inputString = "LURLLLLLDUULRDDDRLRDDDUDDUULLRLULRURLRRDULUUURDUURLRDRRURUURUDDRDLRRLDDDDLLDURLDUUUDRDDDLULLDDLRLRRRLDLDDDDDLUUUDLUULRDUDLDRRRUDUDDRULURULDRUDLDUUUDLUDURUURRUUDRLDURRULURRURUUDDLRLDDDDRDRLDDLURLRDDLUDRLLRURRURRRURURRLLRLDRDLULLUDLUDRURDLRDUUDDUUDRLUDDLRLUDLLURDRUDDLRURDULLLUDDURULDRLUDLUDLULRRUUDDLDRLLUULDDURLURRRRUUDRUDLLDRUDLRRDUDUUURRULLDLDDRLUURLDUDDRLDRLDULDDURDLUUDRRLDRLLLRRRDLLLLURDLLLUDRUULUULLRLRDLULRLURLURRRDRLLDLDRLLRLULRDDDLUDDLLLRRLLLUURLDRULLDURDLULUDLRLDLUDURLLLURUUUDRRRULRDURLLURRLDLRLDLDRRUUDRDDDDDRDUUDULUL\nRRURLURRULLUDUULUUURURULLDLRLRRULRUDUDDLLLRRRRLRUDUUUUDULUDRULDDUDLURLRRLLDLURLRDLDUULRDLLLDLLULLURLLURURULUDLDUDLUULDDLDRLRRUURRRLLRRLRULRRLDLDLRDULDLLDRRULRDRDUDUUUDUUDDRUUUDDLRDULLULDULUUUDDUULRLDLRLUUUUURDLULDLUUUULLLLRRRLDLLDLUDDULRULLRDURDRDRRRDDDLRDDULDLURLDLUDRRLDDDLULLRULDRULRURDURRUDUUULDRLRRUDDLULDLUULULRDRDULLLDULULDUDLDRLLLRLRURUDLUDDDURDUDDDULDRLUDRDRDRLRDDDDRLDRULLURUDRLLUDRLDDDLRLRDLDDUULRUDRLUULRULRLDLRLLULLUDULRLDRURDD\nUUUUUURRDLLRUDUDURLRDDDURRRRULRLRUURLLLUULRUDLLRUUDURURUDRDLDLDRDUDUDRLUUDUUUDDURRRDRUDDUURDLRDRLDRRULULLLUDRDLLUULURULRULDRDRRLURULLDURUURDDRDLLDDDDULDULUULLRULRLDURLDDLULRLRRRLLURRLDLLULLDULRULLDLRULDDLUDDDLDDURUUUURDLLRURDURDUUDRULDUULLUUULLULLURLRDRLLRULLLLRRRRULDRULLUURLDRLRRDLDDRLRDURDRRDDDRRUDRLUULLLULRDDLDRRLRUDLRRLDULULRRDDURULLRULDUDRLRUUUULURLRLRDDDUUDDULLULLDDUDRLRDDRDRLDUURLRUULUULDUDDURDDLLLURUULLRDLRRDRDDDUDDRDLRRDDUURDUULUDDDDUUDDLULLDRDDLULLUDLDDURRULDUDRRUURRDLRLLDDRRLUUUDDUUDUDDDDDDDLULURRUULURLLUURUDUDDULURDDLRDDRRULLLDRRDLURURLRRRDDLDUUDR\nURLLRULULULULDUULDLLRDUDDRRLRLLLULUDDUDLLLRURLLLLURRLRRDLULRUDDRLRRLLRDLRRULDLULRRRRUUDDRURLRUUDLRRULDDDLRULDURLDURLRLDDULURDDDDULDRLLUDRULRDDLUUUDUDUDDRRUDUURUURLUUULRLULUURURRLRUUULDDLURULRRRRDULUDLDRLLUURRRLLURDLDLLDUDRDRLLUDLDDLRLDLRUDUULDRRLLULDRRULLULURRLDLUUDLUDDRLURDDUDRDUDDDULLDRUDLRDLRDURUULRRDRUUULRUURDURLDUDRDLLRUULUULRDDUDLRDUUUUULDDDDDRRULRURLLRLLUUDLUDDUULDRULDLDUURUDUDLRULULUULLLLRLULUDDDRRLLDRUUDRLDDDRDDURRDDDULURDLDLUDDUULUUURDULDLLULRRUURDDUDRUULDLRLURUDLRDLLLDRLDUURUDUDRLLLDDDULLUDUUULLUUUDLRRRURRRRRDUULLUURRDUU\nUDULUUDLDURRUDDUDRDDRRUULRRULULURRDDRUULDRLDUDDRRRRDLRURLLLRLRRLLLULDURRDLLDUDDULDLURLURUURLLLDUURRUUDLLLUDRUDLDDRLRRDLRLDDDULLRUURUUUDRRDLLLRRULDRURLRDLLUDRLLULRDLDDLLRRUDURULRLRLDRUDDLUUDRLDDRUDULLLURLRDLRUUDRRUUDUDRDDRDRDDLRULULURLRULDRURLURLRDRDUUDUDUULDDRLUUURULRDUDRUDRULUDDULLRDDRRUULRLDDLUUUUDUDLLLDULRRLRDDDLULRDUDRLDLURRUUDULUDRURUDDLUUUDDRLRLRLURDLDDRLRURRLLLRDRLRUUDRRRLUDLDLDDDLDULDRLURDURULURUDDDUDUULRLLDRLDDDDRULRDRLUUURD"

// Process Input
let digitStrings = inputString.components(separatedBy: "\n")
let digitInstructions = digitStrings.map { (keypath) -> [Instruction] in
    return keypath.characters.flatMap({ (instruction) -> Instruction? in
        return Instruction(rawValue: String(instruction))
    })
}

// Do the work
var currentDigit = 0x5

let simpleKeyPad:[[Int?]] = [[1,2,3],
                              [4,5,6],
                              [7,8,9]]

let complexKeyPad:[[Int?]] = [[nil, nil, 0x1, nil, nil],
                              [nil, 0x2, 0x3, 0x4, nil],
                              [0x5, 0x6, 0x7, 0x8, 0x9],
                              [nil, 0xA, 0xB, 0xC, nil],
                              [nil, nil, 0xD, nil, nil]]

loopThroughDigits: for digit in digitInstructions {
    for instruction in digit {
        currentDigit = currentDigit.nextDigit(withInstruction: instruction, keypad: complexKeyPad)
    }
    print("\(String(format:"%X", currentDigit))")
}

A straightforward solution using optionals in the keypad.

Generalized the keypad code. There could definitely send to be some error checking.