Advent of Code 2021 in R - Day 4

AdventOfCode2021_d04_main.R

library(tidyverse)

raw_data <- readr::read_lines("days/d04/data.txt") %>%
  stringr::str_trim()

BOARD_SIZE <- 5

draws <- raw_data[1] %>%
  stringr::str_split(",") %>%
  .[[1]] %>%
  as.numeric() %>%
  purrr::accumulate(c)

boards <- raw_data[2:length(raw_data)] %>%
  stringr::str_subset("^$", negate = TRUE) %>%
  split(ceiling(seq_along(.)/BOARD_SIZE)) %>%
  purrr::map(function(x) {
    stringr::str_split(x, "[:space:]+", simplify = T) %>%
      {matrix(as.numeric(.), ncol=ncol(.))}
  })

is_set_in_draw <- function(x, draw)
  length(setdiff(x, draw)) == 0

test_board <- function(draw, board) {
  i <- 1
  while(i <= 5) {
    if (is_set_in_draw(board[i,], draw) |
        is_set_in_draw(board[,i], draw) ) {
      return(TRUE)
    }
    i <- i + 1
  }
  FALSE
}

get_score <- function(draw, board) {
  sum(c(board)[!(c(board) %in% draw)])*draw[length(draw)]
}

# Challenge 1
b <- boards[[1]]
d <- draws[1]
for (draw in draws) {
  tests <- purrr::map_lgl(boards, ~test_board(draw, .))
  if (any(tests)) {
    ib <- which.max(tests) # index of first TRUE board
    winning_board <- boards[[ib]]
    winning_draw <- draw
    break
  }
}
get_score(winning_board, winning_draw)

# Challenge 2
b <- boards[[1]]
d <- draws[1]
for (draw in draws) {
  tests <- purrr::map_lgl(boards, ~test_board(draw, .))
  if (all(tests)) {
    winning_board <- boards[[length(boards)]]
    winning_draw <- draw
    break
  }
  boards <- boards[!tests] # no need to keep already won boards
}
get_score(winning_board, winning_draw)