R/day08.R

In hturner/adventofcode21: Advent of Code Solutions 2021

#' Day 08: Seven Segment Search
#'
#' [Seven Segment Search](https://adventofcode.com/2021/day/8)
#'
#' @name day08
#' @rdname day08
#' @details
#'
#' **Part One**
#'
#' You barely reach the safety of the cave when the whale smashes into the
#' cave mouth, collapsing it. Sensors indicate another exit to this cave at
#' a much greater depth, so you have no choice but to press on.
#'
#' As your submarine slowly makes its way through the cave system, you
#' notice that the four-digit [seven-segment
#' displays](https://en.wikipedia.org/wiki/Seven-segment_display) in your
#' submarine are malfunctioning; [they must have been
#' damaged]{title="Yes, just the four-digit seven-segment ones. Whole batch must have been faulty."}
#' during the escape. You\'ll be in a lot of trouble without them, so
#' you\'d better figure out what\'s wrong.
#'
#' Each digit of a seven-segment display is rendered by turning on or off
#' any of seven segments named `a` through `g`:
#'
#'       0:      1:      2:      3:      4:
#'      aaaa    ....    aaaa    aaaa    ....
#'     b    c  .    c  .    c  .    c  b    c
#'     b    c  .    c  .    c  .    c  b    c
#'      ....    ....    dddd    dddd    dddd
#'     e    f  .    f  e    .  .    f  .    f
#'     e    f  .    f  e    .  .    f  .    f
#'      gggg    ....    gggg    gggg    ....
#'
#'       5:      6:      7:      8:      9:
#'      aaaa    aaaa    aaaa    aaaa    aaaa
#'     b    .  b    .  .    c  b    c  b    c
#'     b    .  b    .  .    c  b    c  b    c
#'      dddd    dddd    ....    dddd    dddd
#'     .    f  e    f  .    f  e    f  .    f
#'     .    f  e    f  .    f  e    f  .    f
#'      gggg    gggg    ....    gggg    gggg
#'
#' So, to render a `1`, only segments `c` and `f` would be turned on; the
#' rest would be off. To render a `7`, only segments `a`, `c`, and `f`
#' would be turned on.
#'
#' The problem is that the signals which control the segments have been
#' mixed up on each display. The submarine is still trying to display
#' numbers by producing output on signal wires `a` through `g`, but those
#' wires are connected to segments *randomly*. Worse, the wire/segment
#' connections are mixed up separately for each four-digit display! (All of
#' the digits *within* a display use the same connections, though.)
#'
#' So, you might know that only signal wires `b` and `g` are turned on, but
#' that doesn\'t mean *segments* `b` and `g` are turned on: the only digit
#' that uses two segments is `1`, so it must mean segments `c` and `f` are
#' meant to be on. With just that information, you still can\'t tell which
#' wire (`b`/`g`) goes to which segment (`c`/`f`). For that, you\'ll need
#' to collect more information.
#'
#' For each display, you watch the changing signals for a while, make a
#' note of *all ten unique signal patterns* you see, and then write down a
#' single *four digit output value* (your puzzle input). Using the signal
#' patterns, you should be able to work out which pattern corresponds to
#' which digit.
#'
#' For example, here is what you might see in a single entry in your notes:
#'
#'     acedgfb cdfbe gcdfa fbcad dab cefabd cdfgeb eafb cagedb ab |
#'     cdfeb fcadb cdfeb cdbaf
#'
#' (The entry is wrapped here to two lines so it fits; in your notes, it
#' will all be on a single line.)
#'
#' Each entry consists of ten *unique signal patterns*, a `|` delimiter,
#' and finally the *four digit output value*. Within an entry, the same
#' wire/segment connections are used (but you don\'t know what the
#' connections actually are). The unique signal patterns correspond to the
#' ten different ways the submarine tries to render a digit using the
#' current wire/segment connections. Because `7` is the only digit that
#' uses three segments, `dab` in the above example means that to render a
#' `7`, signal lines `d`, `a`, and `b` are on. Because `4` is the only
#' digit that uses four segments, `eafb` means that to render a `4`, signal
#' lines `e`, `a`, `f`, and `b` are on.
#'
#' Using this information, you should be able to work out which combination
#' of signal wires corresponds to each of the ten digits. Then, you can
#' decode the four digit output value. Unfortunately, in the above example,
#' all of the digits in the output value (`cdfeb fcadb cdfeb cdbaf`) use
#' five segments and are more difficult to deduce.
#'
#' For now, *focus on the easy digits*. Consider this larger example:
#'
#'     be cfbegad cbdgef fgaecd cgeb fdcge agebfd fecdb fabcd edb |
#'     fdgacbe cefdb cefbgd gcbe
#'     edbfga begcd cbg gc gcadebf fbgde acbgfd abcde gfcbed gfec |
#'     fcgedb cgb dgebacf gc
#'     fgaebd cg bdaec gdafb agbcfd gdcbef bgcad gfac gcb cdgabef |
#'     cg cg fdcagb cbg
#'     fbegcd cbd adcefb dageb afcb bc aefdc ecdab fgdeca fcdbega |
#'     efabcd cedba gadfec cb
#'     aecbfdg fbg gf bafeg dbefa fcge gcbea fcaegb dgceab fcbdga |
#'     gecf egdcabf bgf bfgea
#'     fgeab ca afcebg bdacfeg cfaedg gcfdb baec bfadeg bafgc acf |
#'     gebdcfa ecba ca fadegcb
#'     dbcfg fgd bdegcaf fgec aegbdf ecdfab fbedc dacgb gdcebf gf |
#'     cefg dcbef fcge gbcadfe
#'     bdfegc cbegaf gecbf dfcage bdacg ed bedf ced adcbefg gebcd |
#'     ed bcgafe cdgba cbgef
#'     egadfb cdbfeg cegd fecab cgb gbdefca cg fgcdab egfdb bfceg |
#'     gbdfcae bgc cg cgb
#'     gcafb gcf dcaebfg ecagb gf abcdeg gaef cafbge fdbac fegbdc |
#'     fgae cfgab fg bagce
#'
#' Because the digits `1`, `4`, `7`, and `8` each use a unique number of
#' segments, you should be able to tell which combinations of signals
#' correspond to those digits. Counting *only digits in the output values*
#' (the part after `|` on each line), in the above example, there are `26`
#' instances of digits that use a unique number of segments (highlighted
#' above).
#'
#' *In the output values, how many times do digits `1`, `4`, `7`, or `8`
#' appear?*
#'
#' **Part Two**
#'
#' *(Use have to manually add this yourself.)*
#'
#' *(Try using `convert_clipboard_html_to_roxygen_md()`)*
#'
#' @param x matrix with unique signals in the first 10 columns
#' and signals to be decoded in the last 4 columns
#' @return For Part One, `f08a(x)` returns .... For Part Two,
#'   `f08b(x)` returns ....
#' @export
#' @examples
#' x <- example_data_08()
#' f08a(x)
#' f08b(x)
f08a <- function(x) {
  digits <- nchar(c(x[,11:14]))
  sum(digits %in% c(2, 3, 4, 7))
}


#' @rdname day08
#' @export
f08b <- function(x) {
  # identify key pairs of characters from input
  input <-  x[, 1:10]
  double <- t(input)[nchar(t(input)) == 2]
  triple <- t(input)[nchar(t(input)) == 3]
  quadruple <- t(input)[nchar(t(input)) == 4]
  ## characters in quadruple not in double
  a <- mapply(gsub, paste0("[", double, "]"), "", quadruple)
  ## characters not in triple or quadruple
  b <- mapply(gsub, paste0("[", triple, quadruple, "]"), "", "abcdefg")
  d <- double
  # assign output to digits
  output <- x[, 11:14]
  result <- array(0, dim = dim(output))
  n <- nchar(output)
  result[n == 2] <- 1
  result[n == 3] <- 7
  result[n == 4] <- 4
  result[n == 7] <- 8
  ## 5-character signals that include both characters from key pair
  result[n == 5 & mapply(grepl, paste0("[", a, "].*[", a, "]"), output)] <- 5
  result[n == 5 & mapply(grepl, paste0("[", b, "].*[", b, "]"), output)] <- 2
  result[n == 5 & mapply(grepl, paste0("[", d, "].*[", d, "]"), output)] <- 3
  ## 6-character signals that include only one characters from key pair
  result[n == 6 & mapply(grepl, paste0("^[^", a, "]*[", a, "][^", a, "]*$"),
                         output)] <- 0
  result[n == 6 & mapply(grepl, paste0("^[^", b, "]*[", b, "][^", b, "]*$"),
                         output)] <- 9
  result[n == 6 & mapply(grepl, paste0("^[^", d, "]*[", d, "][^", d, "]*$"),
                         output)] <- 6
  sum(result %*% c(1000, 100, 10, 1))

}


f08_helper <- function(x) {

}


#' @param example Which example data to use (by position or name). Defaults to
#'   1.
#' @rdname day08
#' @export
example_data_08 <- function(example = 1) {
  l <- list(
    a = matrix(c("be", "cfbegad", "cbdgef", "fgaecd", "cgeb", "fdcge", "agebfd", "fecdb", "fabcd", "edb", "fdgacbe", "cefdb", "cefbgd", "gcbe",
                 "edbfga", "begcd", "cbg", "gc", "gcadebf", "fbgde", "acbgfd", "abcde", "gfcbed", "gfec", "fcgedb", "cgb", "dgebacf", "gc",
                 "fgaebd", "cg", "bdaec", "gdafb", "agbcfd", "gdcbef", "bgcad", "gfac", "gcb", "cdgabef", "cg", "cg", "fdcagb", "cbg",
                 "fbegcd", "cbd", "adcefb", "dageb", "afcb", "bc", "aefdc", "ecdab", "fgdeca", "fcdbega", "efabcd", "cedba", "gadfec", "cb",
                 "aecbfdg", "fbg", "gf", "bafeg", "dbefa", "fcge", "gcbea", "fcaegb", "dgceab", "fcbdga", "gecf", "egdcabf", "bgf", "bfgea",
                 "fgeab", "ca", "afcebg", "bdacfeg", "cfaedg", "gcfdb", "baec", "bfadeg", "bafgc", "acf", "gebdcfa", "ecba", "ca", "fadegcb",
                 "dbcfg", "fgd", "bdegcaf", "fgec", "aegbdf", "ecdfab", "fbedc", "dacgb", "gdcebf", "gf", "cefg", "dcbef", "fcge", "gbcadfe",
                 "bdfegc", "cbegaf", "gecbf", "dfcage", "bdacg", "ed", "bedf", "ced", "adcbefg", "gebcd", "ed", "bcgafe", "cdgba", "cbgef",
                 "egadfb", "cdbfeg", "cegd", "fecab", "cgb", "gbdefca", "cg", "fgcdab", "egfdb", "bfceg", "gbdfcae", "bgc", "cg", "cgb",
                 "gcafb", "gcf", "dcaebfg", "ecagb", "gf", "abcdeg", "gaef", "cafbge", "fdbac", "fegbdc", "fgae", "cfgab", "fg", "bagce"),
               byrow = TRUE, ncol = 14)
  )
  l[[example]]
}