2023 - day 16

head(txt)

[1] "\\........-.........\\................................|..................-.............\\../......-.............." 
[2] "........|....\\.../...-...............\\.........\\...........-......-.......\\...../.....................-.../..."
[3] ".......--.......|.-..-..........................\\....../..../........-............/.........|........|........"   
[4] ".................................../.........................|....|.....\\............./..........|...../..\\\\.." 
[5] ".........\\................|..../.........................................-......|........................|...."   
[6] ".|............-....|.....-.....|...............-.............-....................................\\..........."   

Part I

Determine number of energized cells.

R

# txt |> sapply(nchar) |> unname()
# gsub("\\\\", "%%", x = txt) |> sapply(nchar) |> unname()

getcell = function(
    row
    , col
    , lines = txt
){
  
  if (!(row %in% 1:length(txt) & col %in% 1:nchar(lines[1]))){
    s = NA_character_
  } else {
    s = substr(lines[row], start = col, stop = col)
  }
  
  return(s)
  
}

getcell(0, 1)
getcell(5, 1120)
getcell(1, 1)
getcell(1, 2)
getcell(1, 10)


nextcells = function(
    x
    , y
    , from = c("l", "r", "t", "b")
){
  
  from = match.arg(from)
  type = getcell(x, col = y)
  
  if (type == "."){
    if (from == "l") n = c(x, y + 1L)
    else if (from == "r") n = c(x, y - 1L)
    else if (from == "t") n = c(x + 1L, y)
    else if (from == "b") n = c(x - 1L, y)
  } else if (type == "/"){
    if (from == "l") n = c(x - 1L, y)
    else if (from == "r") n = c(x + 1L, y)
    else if (from == "t") n = c(x, y - 1L)
    else if (from == "b") n = c(x, y + 1L)
  } else if (type == "\\"){
    if (from == "l") n = c(x + 1L, y)
    else if (from == "r") n = c(x - 1L, y)
    else if (from == "t") n = c(x, y + 1L)
    else if (from == "b") n = c(x, y - 1L)
  } else if (type == "-"){
    if (from == "l") n = c(x, y + 1L)
    else if (from == "r") n = c(x, y - 1L)
    else if (from == "t") n = c(x, y + 1L, x, y - 1L)
    else if (from == "b") n = c(x, y + 1L, x, y - 1L)
  } else if (type == "|"){
    if (from == "l") n = c(x + 1L, y, x - 1L, y)
    else if (from == "r") n = c(x + 1L, y, x - 1L, y)
    else if (from == "t") n = c(x + 1L, y)
    else if (from == "b") n = c(x - 1L, y)
  }
  
  n = matrix(n, ncol = 2L, byrow = TRUE)
  
  idx = apply(
    n
    , MARGIN = 2L
    , FUN = \(i) which(i == 0)
  ) |> 
    unlist()
  
  if (length(idx) > 0L) n = n[-idx, , drop = FALSE]
  return(n)
  
}

m = matrix(nrow = 0L, ncol = 2L)
colnames(m) = c("row", "col")

n = matrix(c(1L, 1L), ncol = 2L, byrow = TRUE)
colnames(n) = c("row", "col")

while (dim(n)[1] > 0L){
  
  m = rbind(m, n)
  
  for (i in 1:dim(n)[1]){
    n = nextcells(n[i, ])
  }
  
}
rbind(
  m
  , nextcells(m[])
)

txt[1]
x = 1
y = 10
from = "r"
getcell(x, y)

nextcells(1, y = 1, from = "l")
nextcells(1, y = 1, from = "r")
nextcells(1, y = 10, from = "l")
nextcells(1, y = 10, from = "r")
nextcells(1, y = 10, from = "b")
nextcells(1, y = 53, from = "r")
nextcells(1, y = 53, from = "t")
nextcells(1, y = 53, from = "b")
nextcells(1, y = 53, from = "l")

Python

Part II

Add \(m\) successive cards where \(m\) is the number of matches in a card. Get the final number of cards.

R

Python