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Advent of Code 2020-05 with R

colinfay profile image Colin Fay Originally published at colinfay.me on ・1 min read

Solving Advent of Code 2020-05 with R.

[Disclaimer] Obviously, this post contains a big spoiler about Advent of Code.

Instructions

Find the complete instructions at:https://adventofcode.com/2020/day/5.

R solution

Part one

library(magrittr)
# Read the data
ipt <- read.table("2020-05-aoc.txt", header = FALSE, stringsAsFactors = FALSE)

library(magrittr)
# For chunk2
library(stackoverflow)
library(purrr, warn.conflicts = FALSE)
get_chunks <- function(vec, ext, nms){
  # split the vec in two, set the name, and extract the correct chunk
  chunk2(vec, 2) %>%
    setNames(nms) %>%
    pluck(ext)
}

# Prefilling the functions with the correct nms
get_bf<- partial(get_chunks, nms = c("F", "B"))
get_lr <- partial(get_chunks, nms = c("L", "R"))

get_all <- function(entry){
  entry <- strsplit(entry, "")[[1]] 

  # Doing the get_bf on the 7 first letters
  row <- get_bf(0:127, entry[1]) %>%
    get_bf(entry[2]) %>%
    get_bf(entry[3]) %>%
    get_bf(entry[4]) %>%
    get_bf(entry[5]) %>%
    get_bf(entry[6]) %>%
    get_bf(entry[7]) 

  # Doing the get_lr on the 3 last letters
  column <- get_lr(0:7, entry[8]) %>%
    get_lr(entry[9]) %>%
    get_lr(entry[10]) 

  # Computing the seat id
  seatid <- (row * 8) + column   

  return(seatid)
}

# Getting the max
map_dbl(ipt$V1, get_all) %>%
  max()

## [1] 864
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Part two

library(dplyr, warn.conflicts = FALSE)
# Extracting all the ids
map_dbl(ipt$V1, get_all) %>%
  # Sorting them in order and turning into a df
  sort() %>%
  data.frame(
    x = . 
  ) %>%
  # Computing the diff between all ids
  mutate(
    y = lag(x), 
    diff = x - y
  ) %>%
  # My passport ID will be the one between the IDS 
  # of diff != 1
  filter(
    diff != 1
  ) 

##     x   y diff
## 1 740 738 2
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