arnolddustin / AdventOfCode2016

Solutions for Advent of Code 2016

AdventOfCode2016

Day 25

• Unit tests
• Builds upon Day 23 solution, adding new output
• The SignalGenerator class is constructed using the input instructions.
  • The Start(int i) method starts the process at i, which runs until a signal (repeated pattern) is identified (the value in the 'a' register is repeated).
  • When a signal is identified, the generator is stopped, and the signal is inspected to see if it matches the expected signal (0, 1, 0, 1, 0, 1 ...).
  • If the signal doesn't match... the process is repeated at i+1, until a solution is found.
  • If the signal does match... the SignalOutput event (which contains the signal, and the input required to produce the signal) is raised.
• The Solver class is constructed usign the input instructions
  • It creates and wires up an instance of SignalGenerator
  • The Start method is then called on SignalGenerator with an initial value of 0
  • The Solver then waits for the SignalGenerator to raise the SignalOutput event, which contains the solution value.

Day 24

• Unit tests
• Part 1 approach:
  • Use breadth-first search to find shortest routes between all targets
  • Use breadth-first search to find shortest path along those routes inclusive of all targets
• Part 2 uses Part 1, then adds the length of the shortest path back home

Day 23

• Unit tests
• Used and adapted Day12 solution to solve part 1
• Part 2 short-circuits a series of instructions reduce processing time to ~6ms

Day 22

• Unit tests
• Part 2 is broken down into 2 parts:
  • First, the shortest path to moving the empty node to to the target node is determined via a bread-first search
  • Then the steps required to move the goal data to 0,0 is calculate, knowing that 5 moves are required to move the goal data one step to the left
  • Part 2 runs in about 30 seconds.

Day 21

• Unit tests for each operation and combined operations
• For the rotate based on position of letter X instruction reversal, I calculated where each index ends up in part 1, then put those indexes into an array and use it to map sequences when in reverse. I suspect there's an easy way to reverse the original formula.

Day 20

• Unit tests
• Important parts of the solution
  • The MergeRanges method sorts and merges ranges using a Stack<Range>
  • The GetAllowedIps method builds the list of IPs using the Stack<Range>

Day 19

• Unit tests
• Part 1 solution is done using a queue
• Part 2 solution uses math

Day 18

• Unit tests for GetNextRows() and GetSafeTileCount() methods

Day 17

• Unit tests for has generation, allowed directions, shortest, and longest path
• Breadth-first search used to determine shortest and longest paths

Day 16

• Unit tests for dragon curve, checksum, and combined

Day 15

• Unit tests
• The key algorithm is in the Disc class

Day 14

• Unit tests
• Test in part 2 are short-circuited by an Assert.Inconclusive() because they take a while (~5 minutes) to run
• A Dictionary<int, string> is used to cache MD5 hashes for the indexes

Day 13

• Unit tests
• Solver takes the input in the constructor
• Both parts use a bread-first search to calculate steps/locations
• The FindMinimumStepsBetween(int, int, int, int) method finds the minimum steps between two points
• The LocationsWithinSteps(int, int, int) method returns a count of all unique locations reachable within the specified steps

Day 12

• Unit tests
• Solver takes the input in the constructor (along with flag indicating whether it's part 2 or not)
• The GetValueFromRegister(char) method runs the first instruction, then returns the value in the register at the end of the processing chain
• When an instruction is executed, it returns the index of the next instruction

Day 11

• Unit tests
• Part 1 solves in < 1s, and Part 2 in about 20 seconds
• Solver class performs a bread-first search to traverse the tree of moves
• State class represents the state of the building at a give time, and Item instances can be ItemType.Microchip and ItemType.Generator
• This one is more difficult than previous days
  • See the notes in the unit test for details on how equivalent states are determined
  • Spoiler: The magic to this solution is in how State instances are represented during toString()

Day 10

• Unit tests
• Bot and Output classes used to model the problem
• Instructions are processed until all bots have 2 chips to get answer

Day 9

• Unit tests
• See Example1() through Example6() methods for each example
• Part 2 examples working using recursion
• Part2 works with recursion like Part1, but it only keeps track of the length of the strings to keep memory from blowing up.

Day 8

• Run console app with 8 as input for visualization of instructions
• Unit tests
• See SolverUnitTests() method for unit tests for the Screen and Solver classes
• I didn't write anything to interpret the screen for part2...run the unit test and the answer will be written to the console.

Day 7

• Unit tests
• See SolverTests() method for unit tests on internal methods
• Regex used to determine ABBAs and split protocol parts

Day 6

• Unit tests
• Uses linq to find frequency
• This one was really easy

Day 5

• Unit tests
• Uses standard System.Security.Cryptography for MD5
• Note: most of the unit tests have an Assert.Inconclusive() so they will be skipped. These solutions require sequential crypto calls, so they take a while to run.

Day 4

• Unit tests
• Regex is used to extract sector id
• Room holds elements of the room

Day 3

• Unit tests

Day 2

• Unit tests
• Solver gets injected with a keyboard layout
• Tuples used to hold buttons and coordinates

Day 1

• Unit tests
• Vectors and Points are used to hold position
• Solver runs all moves then derives answers from move/location history
• Solver calculates distance to start