Day 5: Print Queue

Reference

library(tidyverse)

# raw <- read_lines(file = "inputs/2024/05.txt")
#raw <- read_lines(file = "test.txt")

Part One

# ordering_rules <- raw[1:(which(raw == "") - 1)]
# updates <- setdiff(raw, ordering_rules)[-1]
# 
# ordering_rules_lookup <- tibble(ordering_rules) |>
#     separate_wider_delim(ordering_rules,
#                          delim = "|",
#                          names = c("page", "page_after")) |> 
#     summarise(page_after = str_flatten(page_after, collapse = ","),
#               .by = page) |> 
#     mutate(page_after = map(page_after, \(x) str_split_1(x, pattern = ",")))
# 
# is_right_order <- function(update_vec) {
#     # index from 2 to end of vector
#     iterator <- seq_along(update_vec)[-1]
#     
#     # message(paste(update_vec, collapse = " "))
#     
#     for (i in iterator) {
#         # message("current number: ", update_vec[i])
#         
#         # retrieve ordering rules for current page
#         following_pages <- ordering_rules_lookup |> 
#             filter(page == update_vec[i]) |> 
#             pull(page_after) |>
#             unlist()
#         
#         # message("dictionary: ", paste(following_pages, collapse = " "))
#         
#         # message("previous elements: ", str_c(update_vec[1:(i-1)], collapse = " "))
#         
#         # intersection can be NULL (element not in LHS of ordering rules)
#         # but length(NULL) = 0, so it's ok
#         intersection <- base::intersect(update_vec[1:(i-1)], following_pages)
#         
#         if (length(intersection) != 0) {
#             return(FALSE)
#         }
#     }
#     
#     return(TRUE)
# }
# 
# tibble(updates_raw = updates,
#        update_vec = map(updates_raw, \(x) str_split_1(x, pattern = ",")),
#        right_order = map_lgl(update_vec, is_right_order)) |> 
#     filter(right_order) |> 
#     mutate(mid_page = map_chr(update_vec, \(x) x[ceiling(length(x)/2)]),
#            mid_page = as.integer(mid_page)) |> 
#     summarise(total = sum(mid_page)) |> 
#     pull(total) |> 
#     cat()

Part Two

# tibble(updates_raw = updates,
#        update_vec = map(updates_raw, \(x) str_split_1(x, pattern = ",")),
#        right_order = map_lgl(update_vec, is_right_order)) |> 
#     filter(!right_order)

# input <- read_lines("test.txt")
# 
# sep <- which(input == "")
# 
# rules <- input[seq(1, sep - 1)] |>
#   strsplit("\\|") |>
#   lapply(as.integer)
# updates <- input[seq(sep + 1, length(input))] |>
#   strsplit(",") |>
#   lapply(as.integer)
# 
# pass_rule <- function(rule, update) {
#   order <- diff(match(rule, update))
# 
#   is.na(order) || order > 0
# }
# 
# pass_rules <- function(update, rules) {
#   all(vapply(rules, pass_rule, logical(1), update = update))
# }
# 
# which_passes <- vapply(updates, pass_rules, logical(1), rules)
# 
# get_middle <- function(x) {
#   mid <- length(x) / 2 + 1
#   x[mid]
# }
# 
# uncorrect <- updates[!which_passes]
# 
# fix_order <- function(rule, update) {
#     browser()
#   matches <- match(rule, update)
#   before <- matches[1]
#   after <- matches[2]
#   
#   before_inds <- setdiff(seq(1, before), after)
#   
#   after_inds <- setdiff(seq_along(update), c(before_inds, after))
#   
#   new_order <- c(before_inds, after, after_inds)
#   update[new_order]
# }
# 
# fix_update <- function(update, rules) {
#   while (!pass_rules(update, rules)) {
#     for (rule in rules) {
#       if (pass_rule(rule, update)) {
#         next
#       }
#       update <- fix_order(rule, update)
#     }
#   }
#   update
# }
# 
# uncorrect |>
#   lapply(fix_update, rules) |>
#   lapply(get_middle) |>
#   unlist() |>
#   sum()