Day 5

AdventOfCode > 2024

suppressPackageStartupMessages({
  library(tidyverse)
  library(httr2)
})
adventofcode_input <- \(
  year, day, what = c("data.frame", "character", "matrix"), input = NULL
) {
  if (is.null(input)) {
    session <- Sys.getenv("ADVENT_SESSION")
    if (session == "") {
      stop("Must set ADVENT_SESSION in .Renviron")
    }
    url <- paste0("https://adventofcode.com/", year, "/day/", day, "/input")
    tryCatch({
        res <- request(url) |> 
            req_cookies_set(session = session) |> 
            req_perform() |> 
            resp_body_string(encoding = "UTF-8")
        },
        error = \(e) stop("Error getting the input file")
    )
  } else {
    res <- input
  }
  if(what[1] == "character") {
    return(res)
  }
  df <- data.frame(x = res |> strsplit("\n") |>  unlist())
  if(what[1] == "data.frame") {
    return(df)
  }    
  if(what[1] == "matrix") {
    ret <- df$x |> 
      stringr::str_split("")
    m <- do.call(rbind, ret)
    return(m)
  }   
}

Part 1

test <- "47|53
97|13
97|61
97|47
75|29
61|13
75|53
29|13
97|29
53|29
61|53
97|53
61|29
47|13
75|47
97|75
47|61
75|61
47|29
75|13
53|13

75,47,61,53,29
97,61,53,29,13
75,29,13
75,97,47,61,53
61,13,29
97,13,75,29,47"

input <- adventofcode_input(what = "data.frame", input = test)
rules <- 
  input |> 
  filter(row_number() < which(x == "")) |> 
  separate_wider_delim(x, "|", names_sep = "") |>
  print()

# A tibble: 21 × 2
   x1    x2   
   <chr> <chr>
 1 47    53   
 2 97    13   
 3 97    61   
 4 97    47   
 5 75    29   
 6 61    13   
 7 75    53   
 8 29    13   
 9 97    29   
10 53    29   
# ℹ 11 more rows

updates <- input |> 
  filter(row_number() > which(x == "")) |> 
  mutate(
    x = map(x, \(x) x |> 
      str_split_1(",") |>
      as.numeric()
    )
  ) |> 
  pull(x)

n_incorrect_rules <- \(u, rules) {
  rules |> 
    filter((x1 %in% u) & (x2 %in% u)) |> 
    rowwise() |> 
    mutate(posx1 = which(u == x1), posx2 = which(u == x2)) |> 
    ungroup() |>
    filter(posx1 > posx2) |> 
    nrow()
}

sum(map_dbl(updates, \(i) {
  if(n_incorrect_rules(i, rules) == 0) {
      i[(1+length(i))/2]
  } else {
    0
  }
}))

[1] 143

input <- adventofcode_input(2024, 5, what = "data.frame")

rules <- 
  input |> 
  filter(row_number() < which(x == "")) |> 
  separate_wider_delim(x, "|", names_sep = "")

updates <- input |> 
  filter(row_number() > which(x == "")) |> 
  mutate(
    x = map(x, \(x) x |> 
      str_split_1(",") |>
      as.numeric()
    )
  ) |> 
  pull(x)

n_incorrect_rules <- \(u, rules) {
  rules |> 
    filter((x1 %in% u) & (x2 %in% u)) |> 
    rowwise() |> 
    mutate(posx1 = which(u == x1), posx2 = which(u == x2)) |> 
    ungroup() |>
    filter(posx1 > posx2) |> 
    nrow()
}

sum(map_dbl(updates, \(i) {
  if(n_incorrect_rules(i, rules) == 0) {
      i[(1+length(i))/2]
  } else {
    0
  }
}))

[1] 5732

Part 2

test <- "47|53
97|13
97|61
97|47
75|29
61|13
75|53
29|13
97|29
53|29
61|53
97|53
61|29
47|13
75|47
97|75
47|61
75|61
47|29
75|13
53|13

75,47,61,53,29
97,61,53,29,13
75,29,13
75,97,47,61,53
61,13,29
97,13,75,29,47"

input <- adventofcode_input(what = "data.frame", input = test)

rules <- 
  input |> 
  filter(row_number() < which(x == "")) |> 
  separate_wider_delim(x, "|", names_sep = "")

updates <- input |> 
  filter(row_number() > which(x == "")) |> 
  mutate(
    x = map(x, \(x) x |> 
      str_split_1(",") |>
      as.numeric()
    )
  ) |> 
  pull(x)

incorrect_rules <- \(u, rules) {
  rules |> 
    filter((x1 %in% u) & (x2 %in% u)) |> 
    rowwise() |> 
    mutate(posx1 = which(u == x1), posx2 = which(u == x2)) |> 
    ungroup() |>
    filter(posx1 > posx2)
}

n_incorrect_rules <- \(u, rules) {
  incorrect_rules(u, rules) |>    
    nrow()
}


generate_permutations <- function(vec) {
  n <- length(vec)
  grid <- expand.grid(rep(list(vec), n))
  valid_perms <- grid[apply(grid, 1, function(row) length(unique(row)) == n), ] 
  valid_perms |> 
    rowwise() |> 
    group_split() |> 
    map(as.numeric)  
}

correct_update <- \(u, rules) {
  candidates <- generate_permutations(u)
  for(i in seq_along(candidates)) {
      candidate <- candidates[[i]]      
      if(n_incorrect_rules(candidate, rules) == 0){
        return(candidate)
      }
  }
  stop("We didn't find a solution.")
}
# correct_update(c(61, 13, 29), rules)
# correct_update(c(97, 13, 75, 29, 47), rules)

sum(map_dbl(updates, \(i) {
  incorrect <- incorrect_rules(i, rules)
  if(nrow(incorrect) > 0) {    
      fixed <- correct_update(i, rules)
      return(fixed[(1+length(fixed))/2])
  }
  0  
}))

[1] 123

input <- adventofcode_input(2024, 5, what = "data.frame")

rules <- input |> 
  filter(row_number() < which(x == "")) |> 
  separate_wider_delim(x, "|", names_sep = "")

updates <- input |> 
  filter(row_number() > which(x == "")) |> 
  mutate(x = map(x, \(x) x |> str_split_1(",") |> as.numeric())) |> 
  pull(x)

incorrect_rules <- \(u, rules) {
  rules |> 
    filter((x1 %in% u) & (x2 %in% u)) |> 
    rowwise() |> 
    mutate(posx1 = which(u == x1), posx2 = which(u == x2)) |> 
    ungroup() |> 
    filter(posx1 > posx2)
}

correct_update <- \(u, rules) {  
  # print(u)
  i <- 1
  repeat {
    to_fix <- incorrect_rules(u, rules)
    if(nrow(to_fix) == 0) return(u)
    current <- to_fix[1, ]    
    u[c(current$posx2, current$posx1)] <- u[c(current$posx1, current$posx2)]        
    i <- i + 1
    # print(i)
  }
}
# correct_update(c(97, 13, 75, 29, 47), rules)

sum(map_dbl(updates, \(i) {
  incorrect <- incorrect_rules(i, rules)
  if(nrow(incorrect) > 0) {    
      fixed <- correct_update(i, rules)
      return(fixed[(1+length(fixed))/2])
  }
  0  
}))

[1] 4716