# Parts 1 and 2

``````library(tidyverse)

# rotate matrix 90° clockwise
rotate <- function(mat, n = 1) {
i <- 0
while (i < n) {
mat <- t(apply(mat, 2, rev))
i <- i + 1
}
mat
}

# create a mirror image of the matrix
flip <- function(mat) {
t(apply(mat, 1, rev))
}

# convert enhancement rule string into matrix
string_to_mat <- function(ii) {
uu <- strsplit(ii, "/")[[1]]
s <- nchar(uu[1])
uu <- unlist(strsplit(uu, ""))
matrix(uu, ncol = s, byrow = TRUE)
}

# convert matrix into enhancement rule string
mat_to_string <- function(m) {
paste(apply(m, 1, paste, collapse = ""),
collapse = "/")
}

# from an enhacement string, find all possible combinations
expand_combinations <- function(ii) {
m <- string_to_mat(ii)
s <- dim(m)[1]
mr <- vector("list", 4)
for (i in 0:3) {
mr[[(i*2) + 1]] <- rotate(m, i + 1)
mr[[(i*2) + 2]] <- rotate(flip(m), i + 1)
}
map_chr(mr, mat_to_string)
}

# create data frame from input, and include all unique combinations
col_names = FALSE) %>%
mutate_all(~ gsub(">?\\s+", "", .)) %>%
set_names(c("ii", "oo")) %>%
mutate(comb = map(ii, ~ expand_combinations(.))) %>%
unnest() %>%
distinct(comb, .keep_all = TRUE)
}

# split a matrix into a list that contains 2x2 or 3x3
split_mat <- function(m, n) {
n_mat <- dim(m)[1] / n
res <- vector("list", n_mat^2)
idx_start <- seq(1, to = dim(m)[1], by = n)
k <- 1
for (i in idx_start) {
for (j in idx_start) {
res[[k]] <- m[i:(i + n - 1), j:(j + n - 1)]
k <- k + 1
}
}
res
}

# reassamble a matrix from a list of 2x2 or 3x3 matrices
list_to_mat <- function(lst) {
si <- nrow(lst[[1]])
s <- si * sqrt(length(lst))
res <- array(, dim = c(s, s))
idx_start <- seq(1, to = s, by = si)
k <- 1
for (i in idx_start) {
for (j in idx_start) {
res[i:(i + si - 1), j:(j + si - 1)] <- lst[[k]]
k <- k + 1
}
}
res
}

# use the enhancement rule book to grow the matrix
convert_rule <- function(pattern, rules) {
res <- rules\$oo[rules\$comb == pattern]
if (nchar(res) ==  0) stop("problem...")
string_to_mat(res)
}

# apply the enhacement algo for a set of rules, and n iterations
enhance <- function(rules, n) {
i <- 0
d <- c(2, 3)
start <- c(".#./..#/###")
m <- string_to_mat(start)

while (i < n) {
s <- dim(m)[1]
sp <- d[s %% d == 0][1]
smat <- split_mat(m, sp)
sstr <- map(smat, mat_to_string)
mlst <- map(sstr, convert_rule, rules)
m <- list_to_mat(mlst)
i <- i + 1
}
m
}

``````
``````## Parsed with column specification:
## cols(
##   X1 = col_character(),
##   X2 = col_character()
## )
``````
``````part1 <- enhance(rules, 5)
sum(part1 == "#")
``````
``````## [1] 190
``````
``````part2 <- enhance(rules, 18)
sum(part2 == "#")
``````
``````## [1] 2335049
``````

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