2021-11: Dumbo Octopus

library(tidyverse)

── Attaching packages ─────────────────────────────────────── tidyverse 1.3.2 ──
✔ ggplot2 3.4.0      ✔ purrr   0.3.5 
✔ tibble  3.1.8      ✔ dplyr   1.0.10
✔ tidyr   1.2.1      ✔ stringr 1.4.1 
✔ readr   2.1.3      ✔ forcats 0.5.2 
── Conflicts ────────────────────────────────────────── tidyverse_conflicts() ──
✖ dplyr::filter() masks stats::filter()
✖ dplyr::lag()    masks stats::lag()

library(data.table)

Attaching package: 'data.table'

The following objects are masked from 'package:dplyr':

    between, first, last

The following object is masked from 'package:purrr':

    transpose

octopusM <- readLines("input.txt")

Part 1

octopus <- octopusM |>
  strsplit("") %>%
  do.call(rbind, .) |>
  as.matrix() |>
  apply(1, as.numeric) |>
  t()

octopusCol <- ncol(octopus)
octopusRow <- nrow(octopus)

flash_counter <- 0

get_adjacent <- function(xx, yy, ncol, nrow) {
  x <- xx; y <- yy
  x <- (x-1):(x+1); y <- (y-1):(y+1)
  
  x <- x[sapply(x, \(j) between(j, 1, ncol))]
  y <- y[sapply(y, \(j) between(j, 1, nrow))]

  expand.grid("col" = x, "row" = y) |>
    filter(!(col == xx & row == yy)) |>
    as.matrix()
}

for(i in 1:100) {
  octopus <- octopus + 1
  
  while(any(octopus > 9)) {
    flash <- which(octopus > 9, arr.ind = TRUE)
    octopus[octopus > 9] <- 0
    for(x in 1:nrow(flash)) {
      adj <- 
        get_adjacent(flash[x, "col"], flash[x, "row"], octopusCol, octopusRow)
      
      octopus[adj[,"row"], adj[,"col"]] <- 
        apply(octopus[adj[,"row"], adj[,"col"]], c(1, 2), 
              \(x) { ifelse(x == 0, 0, x + 1) })
    }
  }
  flash_counter <<- flash_counter + length(octopus[octopus == 0])
}
flash_counter

[1] 1603

Part 2

octopus <- octopusM |>
  strsplit("") %>%
  do.call(rbind, .) |>
  as.matrix() |>
  apply(1, as.numeric) |>
  t()

i <- 1

while(TRUE) {
  octopus <- octopus + 1
  
  while(any(octopus > 9)) {
    flash <- which(octopus > 9, arr.ind = TRUE)
    octopus[octopus > 9] <- 0
    for(x in 1:nrow(flash)) {
      adj <- 
        get_adjacent(flash[x, "col"], flash[x, "row"], octopusCol, octopusRow)
      
      octopus[adj[,"row"], adj[,"col"]] <- 
        apply(octopus[adj[,"row"], adj[,"col"]], c(1, 2), 
              \(x) { ifelse(x == 0, 0, x + 1) })
    }
  }
  if (length(octopus[octopus == 0]) == octopusRow * octopusCol) {
    print(i)
    break
  } else { i <- i + 1 }
}

[1] 222