Nathan Moore

Advent of Code 2020

This is a short review of my first foray into Advent of Code. I’ve started to gather my thoughts in the github readme while looking over the code again. I had big goals of completing each day in R and python, but after a few days decided that one language was more than enough. It will be an ongoing project to look at each day and see if I can write python solutions, while also collecting choice tidbits of fancy or useful or awful code.

This is the advent website: Advent of Code 2020

This is my github repository: github.com/nmoorenz/advent-of-code

The following is a comparison of R and Python code for day 5, my favourite day of the challenge. Recognising the ticket numbers can be interpreted in binary is a crucial breakthrough. I love finding a new and good function in R: strtoi(). That takes a base argument for binary! Then finding int() in Python has the same argument. List comprehensions are, for me, a killer feature of Python.

R Code

# tidyverse of course
suppressPackageStartupMessages(library(tidyverse))

# love the here package to load things
inputfile = here::here("static", "data", "advent2020", "day05.txt")
bp <- read.delim(inputfile, header = FALSE)

# conversions for letters to binary
named_v = c("F" = "0", "B" = "1", "L" = "0", "R" = "1")

# mutate seems like the best way to do this
# we can also use many replacements in one function
# strtoi() for string to integer, in base 2
bp_bin <- bp %>% 
  mutate(
    bin = str_replace_all(V1, named_v),
    row = strtoi(str_sub(bin, end = 7), base = 2), 
    col = strtoi(str_sub(bin, start = 8), base = 2), 
    id = row * 8 + col
  )

# max is part one answer
max_id <- max(bp_bin$id)  
min_id <- min(bp_bin$id)

# possible seats from min to max
bp_seq = seq(from = min_id, to = max_id)

# part two answer - seat left over
p2 <- setdiff(bp_seq, bp_bin$id)

Python Code

# read file
with open("../../../static/data/advent2020/day05.txt", "r") as f:
  bp = f.read().splitlines()

# row and col binary via replacement
row = [x[:7].replace("B", "1").replace("F", "0") for x in bp]
col = [x[7:].replace("L", "0").replace("R", "1") for x in bp]

# id as a combo of row and col            
id = [int(r, 2) * 8 + int(c, 2) for r, c in zip(row, col)]

#part a
p1 = max(id)

# part b
p2 = set(range(min(id), max(id))) - set(id)

Answer

The maximum seat number on my plane (part one answer) is 826 and my seat number (part two answer) is 678.

In honour of the card playing crab mentioned in the challenges, here’s a big one from the Te Papa collection, only included here for creating a picture for the blog page.

Image Credit: Charybdis (Charybdis) japonica (A. Milne-Edwards, 1861), collected September 2000, Auckland, Rangitoto Channel, New Zealand. CC BY 4.0. Te Papa (CR.009843)

Crab
Crab