R/day13.R

In hturner/adventofcode21: Advent of Code Solutions 2021

#' Day 13: Transparent Origami
#'
#' [Transparent Origami](https://adventofcode.com/2021/day/13)
#'
#' @name day13
#' @rdname day13
#' @details
#'
#' **Part One**
#'
#' You reach another volcanically active part of the cave. It would be nice
#' if you could do some kind of thermal imaging so you could tell ahead of
#' time which caves are too hot to safely enter.
#'
#' Fortunately, the submarine seems to be equipped with a thermal camera!
#' When you activate it, you are greeted with:
#'
#'     Congratulations on your purchase! To activate this infrared thermal imaging
#'     camera system, please enter the code found on page 1 of the manual.
#'
#' Apparently, the Elves have never used this feature. To your surprise,
#' you manage to find the manual; as you go to open it, page 1 falls out.
#' It\'s a large sheet of [transparent
#' paper](https://en.wikipedia.org/wiki/Transparency_(projection))! The
#' transparent paper is marked with random dots and includes instructions
#' on how to fold it up (your puzzle input). For example:
#'
#'     6,10
#'     0,14
#'     9,10
#'     0,3
#'     10,4
#'     4,11
#'     6,0
#'     6,12
#'     4,1
#'     0,13
#'     10,12
#'     3,4
#'     3,0
#'     8,4
#'     1,10
#'     2,14
#'     8,10
#'     9,0
#'
#'     fold along y=7
#'     fold along x=5
#'
#' The first section is a list of dots on the transparent paper. `0,0`
#' represents the top-left coordinate. The first value, `x`, increases to
#' the right. The second value, `y`, increases downward. So, the coordinate
#' `3,0` is to the right of `0,0`, and the coordinate `0,7` is below `0,0`.
#' The coordinates in this example form the following pattern, where `#` is
#' a dot on the paper and `.` is an empty, unmarked position:
#'
#'     ...#..#..#.
#'     ....#......
#'     ...........
#'     #..........
#'     ...#....#.#
#'     ...........
#'     ...........
#'     ...........
#'     ...........
#'     ...........
#'     .#....#.##.
#'     ....#......
#'     ......#...#
#'     #..........
#'     #.#........
#'
#' Then, there is a list of *fold instructions*. Each instruction indicates
#' a line on the transparent paper and wants you to fold the paper *up*
#' (for horizontal `y=...` lines) or *left* (for vertical `x=...` lines).
#' In this example, the first fold instruction is `fold along y=7`, which
#' designates the line formed by all of the positions where `y` is `7`
#' (marked here with `-`):
#'
#'     ...#..#..#.
#'     ....#......
#'     ...........
#'     #..........
#'     ...#....#.#
#'     ...........
#'     ...........
#'     -----------
#'     ...........
#'     ...........
#'     .#....#.##.
#'     ....#......
#'     ......#...#
#'     #..........
#'     #.#........
#'
#' Because this is a horizontal line, fold the bottom half *up*. Some of
#' the dots might end up overlapping after the fold is complete, but dots
#' will never appear exactly on a fold line. The result of doing this fold
#' looks like this:
#'
#'     #.##..#..#.
#'     #...#......
#'     ......#...#
#'     #...#......
#'     .#.#..#.###
#'     ...........
#'     ...........
#'
#' Now, only `17` dots are visible.
#'
#' Notice, for example, the two dots in the bottom left corner before the
#' transparent paper is folded; after the fold is complete, those dots
#' appear in the top left corner (at `0,0` and `0,1`). Because the paper is
#' transparent, the dot just below them in the result (at `0,3`) remains
#' visible, as it can be seen through the transparent paper.
#'
#' Also notice that some dots can end up *overlapping*; in this case, the
#' dots merge together and become a single dot.
#'
#' The second fold instruction is `fold along x=5`, which indicates this
#' line:
#'
#'     #.##.|#..#.
#'     #...#|.....
#'     .....|#...#
#'     #...#|.....
#'     .#.#.|#.###
#'     .....|.....
#'     .....|.....
#'
#' Because this is a vertical line, fold *left*:
#'
#'     #####
#'     #...#
#'     #...#
#'     #...#
#'     #####
#'     .....
#'     .....
#'
#' The instructions made a square!
#'
#' The transparent paper is pretty big, so for now, focus on just
#' completing the first fold. After the first fold in the example above,
#' `17` dots are visible - dots that end up overlapping after the fold is
#' completed count as a single dot.
#'
#' *How many dots are visible after completing just the first fold
#' instruction on your transparent paper?*
#'
#' **Part Two**
#'
#' *(Use have to manually add this yourself.)*
#'
#' *(Try using `convert_clipboard_html_to_roxygen_md()`)*
#'
#' @param coord data frame of co-ordinates
#' @param instructions chanracter vector of instructions
#' @return For Part One, `f13a(x)` returns .... For Part Two,
#'   `f13b(x)` returns ....
#' @export
#' @examples
#' f13a(example_data_13(1), example_data_13(2))
#' f13b(example_data_13(1), example_data_13(2))
f13a <- function(coord, instructions) {
  coord <- coord + 1
  dim_x <- rev(vapply(coord, max, numeric(1)))
  x <- array(FALSE, dim = dim_x)
  x[as.matrix(coord[c(2,1)])] <- TRUE
  direction <- gsub("fold along ([xy])=[0-9]", "\\1", instructions)
  pos <- as.numeric(gsub("fold along [xy]=([0-9].*)", "\\1", instructions)) + 1
  if (direction[1] == "y"){
    x <- x[seq(pos[1] - 1),] | x[dim_x[1]:(pos[1] + 1),]
  } else {
    x <- x[,seq(pos[1] - 1)] | x[,dim_x[2]:(pos[1] + 1)]
  }
  sum(x)
}


#' @rdname day13
#' @export
f13b <- function(coord, instructions) {
  coord <- coord + 1
  dim_x <- rev(vapply(coord, max, numeric(1)))
  x <- array(FALSE, dim = dim_x)
  x[as.matrix(coord[c(2,1)])] <- TRUE
  direction <- gsub("fold along ([xy])=[0-9].*", "\\1", instructions)
  pos <- as.numeric(gsub("fold along [xy]=([0-9].*)", "\\1", instructions)) + 1
  for (i in seq_along(pos)){
    if (direction[i] == "y"){
      x <- x[seq(pos[i] - 1),] | x[dim_x[1]:(pos[i] + 1),]
      dim_x[1] <- pos[i] - 1
    } else {
      x <- x[,seq(pos[i] - 1)] | x[,dim_x[2]:(pos[i] + 1)]
      dim_x[2] <- pos[i] - 1
    }
  }
  x
}


f13_helper <- function(x) {

}


#' @param example Which example data to use (by position or name). Defaults to
#'   1.
#' @rdname day13
#' @export
example_data_13 <- function(example = 1) {
  l <- list(
    a = data.frame(x = c(6, 0, 9, 0, 10, 4, 6, 6, 4, 0,
                         10, 3, 3, 8, 1, 2, 8, 9),
                  y = c(10, 14, 10, 3, 4, 11, 0, 12, 1,
                        13, 12, 4, 0, 4, 10, 14, 10, 0)),
    b = c("fold along y=7", "fold along x=5")
  )
  l[[example]]
}