Post: Advent of Code 2017 intro
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Jez Cope
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title: "Advent of Code 2017: introduction"
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description: "In which I plan to take part in the annual daily coding challenge for the month of December."
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slug: advent-of-code-2017
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date: 2017-11-29T18:33:08+00:00
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tags:
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- Technology
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- Learning
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- Advent of Code
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- Python
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- Haskell
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- Emacs
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---
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It's a common lament of mine that I don't get to write a lot of code in my day-to-day job. I like the feeling of making something from nothing, and I often look for excuses to write bits of code, both at work and outside it.
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[Advent of Code][] is a daily series of programming challenges for the month of December, and is about to start its third annual incarnation. I discovered it too late to take part in any serious way last year, but I'm going to give it a try this year.
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[Advent of Code]: http://adventofcode.com
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There are no restrictions on programming language (so of course some people delight in using esoteric languages like [Brainf**k](https://en.wikipedia.org/wiki/Brainfuck)), but I think I'll probably stick with Python for the most part. That said, I miss my Haskell days and I'm intrigued by new kids on the block Go and Rust, so I might end up throwing in a few of those on some of the simpler challenges.
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I'd like to focus a bit more on *how* I solve the puzzles. They generally come in two parts, with the second part only being revealed after successful completion of the first part. With that in mind, test-driven development makes a lot of sense, because I can verify that I haven't broken the solution to the first part in modifying to solve the second.
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I may also take a literate programming approach with `org-mode` or Jupyter notebooks to document my solutions a bit more, and of course that will make it easier to publish solutions here so I'll do that as much as I can make time for.
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---
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On that note, here are some solutions for 2016 that I've done recently as a warmup.
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## Day 1: Python
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[Day 1 instructions](http://adventofcode.com/2016/day/1)
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```python
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import numpy as np
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import pytest as t
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import sys
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TURN = {
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'L': np.array([[0, 1],
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[-1, 0]]),
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'R': np.array([[0, -1],
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[1, 0]])
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}
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ORIGIN = np.array([0, 0])
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NORTH = np.array([0, 1])
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class Santa:
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def __init__(self, location, heading):
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self.location = np.array(location)
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self.heading = np.array(heading)
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self.visited = [(0,0)]
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def execute_one(self, instruction):
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start_loc = self.location.copy()
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self.heading = self.heading @ TURN[instruction[0]]
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self.location += self.heading * int(instruction[1:])
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self.mark(start_loc, self.location)
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def execute_many(self, instructions):
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for i in instructions.split(','):
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self.execute_one(i.strip())
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def distance_from_start(self):
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return sum(abs(self.location))
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def mark(self, start, end):
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for x in range(min(start[0], end[0]), max(start[0], end[0])+1):
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for y in range(min(start[1], end[1]), max(start[1], end[1])+1):
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if any((x, y) != start):
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self.visited.append((x, y))
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def find_first_crossing(self):
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for i in range(1, len(self.visited)):
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for j in range(i):
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if self.visited[i] == self.visited[j]:
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return self.visited[i]
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def distance_to_first_crossing(self):
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crossing = self.find_first_crossing()
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if crossing is not None:
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return abs(crossing[0]) + abs(crossing[1])
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def __str__(self):
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return f'Santa @ {self.location}, heading {self.heading}'
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def test_execute_one():
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s = Santa(ORIGIN, NORTH)
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s.execute_one('L1')
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assert all(s.location == np.array([-1, 0]))
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assert all(s.heading == np.array([-1, 0]))
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s.execute_one('L3')
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assert all(s.location == np.array([-1, -3]))
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assert all(s.heading == np.array([0, -1]))
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s.execute_one('R3')
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assert all(s.location == np.array([-4, -3]))
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assert all(s.heading == np.array([-1, 0]))
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s.execute_one('R100')
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assert all(s.location == np.array([-4, 97]))
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assert all(s.heading == np.array([0, 1]))
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def test_execute_many():
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s = Santa(ORIGIN, NORTH)
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s.execute_many('L1, L3, R3')
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assert all(s.location == np.array([-4, -3]))
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assert all(s.heading == np.array([-1, 0]))
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def test_distance():
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assert Santa(ORIGIN, NORTH).distance_from_start() == 0
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assert Santa((10, 10), NORTH).distance_from_start() == 20
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assert Santa((-17, 10), NORTH).distance_from_start() == 27
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def test_turn_left():
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east = NORTH @ TURN['L']
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south = east @ TURN['L']
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west = south @ TURN['L']
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assert all(east == np.array([-1, 0]))
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assert all(south == np.array([0, -1]))
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assert all(west == np.array([1, 0]))
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def test_turn_right():
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west = NORTH @ TURN['R']
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south = west @ TURN['R']
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east = south @ TURN['R']
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assert all(east == np.array([-1, 0]))
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assert all(south == np.array([0, -1]))
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assert all(west == np.array([1, 0]))
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if __name__ == '__main__':
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instructions = sys.stdin.read()
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santa = Santa(ORIGIN, NORTH)
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santa.execute_many(instructions)
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print(santa)
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print('Distance from start:', santa.distance_from_start())
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print('Distance to target: ', santa.distance_to_first_crossing())
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```
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## Day 2: Haskell
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[Day 2 instructions](http://adventofcode.com/2016/day/2)
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```haskell
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module Main where
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data Pos = Pos Int Int deriving (Show)
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-- Magrittr-style pipe operator
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(|>) :: a -> (a -> b) -> b
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x |> f = f x
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swapPos :: Pos -> Pos
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swapPos (Pos x y) = Pos y x
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clamp :: Int -> Int -> Int -> Int
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clamp lower upper x | x < lower = lower
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| x > upper = upper
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| otherwise = x
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clampH :: Pos -> Pos
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clampH (Pos x y) = Pos x' y'
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where y' = clamp 0 4 y
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r = abs (2 - y')
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x' = clamp r (4-r) x
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clampV :: Pos -> Pos
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clampV = swapPos . clampH . swapPos
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buttonForPos :: Pos -> String
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buttonForPos (Pos x y) = [buttons !! y !! x]
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where buttons = [" D ",
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" ABC ",
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"56789",
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" 234 ",
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" 1 "]
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decodeChar :: Pos -> Char -> Pos
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decodeChar (Pos x y) 'R' = clampH $ Pos (x+1) y
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decodeChar (Pos x y) 'L' = clampH $ Pos (x-1) y
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decodeChar (Pos x y) 'U' = clampV $ Pos x (y+1)
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decodeChar (Pos x y) 'D' = clampV $ Pos x (y-1)
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decodeLine :: Pos -> String -> Pos
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decodeLine p "" = p
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decodeLine p (c:cs) = decodeLine (decodeChar p c) cs
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makeCode :: String -> String
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makeCode instructions = lines instructions -- split into lines
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|> scanl decodeLine (Pos 1 1) -- decode to positions
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|> tail -- drop start position
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|> concatMap buttonForPos -- convert to buttons
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main = do
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input <- getContents
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putStrLn $ makeCode input
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```
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