Advent of Code 2021 - Day 6

Aloha, who heard of lanternfish before? Me neither.

Part 1:

initial_state <- readLines(con = "day_six_one")
initial_state <- as.integer(unlist(strsplit(initial_state, split =",")))

sim_fish_faster <- function(ini_state = c(3L, 4L, 3L, 1L, 2L), n_run = 18L, vec_length = 1e4) {
  m <- 1L
  fish_vec <- rep(NA_integer_, vec_length)
  fish_vec[1 : length(ini_state)] <- ini_state
  update_max <- min(which(is.na(fish_vec)))
  while(m <= n_run) {
    fish_vec   <- fish_vec - 1L
    new_fish_n <- sum(fish_vec < 0L, na.rm = TRUE)
    fish_vec[fish_vec < 0L] <- 6L
    
    if(new_fish_n > 0) {
      fish_vec[update_max: (new_fish_n + update_max - 1L)] <- 8L
      update_max <- min(which(is.na(fish_vec)))
    } else {
      
    }
    m <- m + 1L
  }
  
  return(na.omit(fish_vec))
}

fish_state <- sim_fish_faster(ini_state = initial_state, n_run = 80L, vec_length = 1e7)
length(fish_state)

## [1] 362740

Part 2:

To be updatet