Advent of Code 2021 - Day 4

Aloha, welcome to fourth day of Advent of Code 2021. Playing Bingo against a giant squid turned out to be more of struggle than I anticipated. I wanted to avoid loops for this puzzle and ended with a solution, which is a little bit hard to understand. Nevertheless, here it comes:

rand_n   <- read.csv(file = "day_four_seq", header = FALSE, sep = ",")
rand_seq <- as.integer(rand_n[1,])

#read the matrices
mat_n <- lapply(1 : 100, function(x){
  as.matrix(read.csv(file = "day_four_mat", nrows = 5L, skip = (x - 1L) * 6L , 
           sep = "", header = FALSE))
})

Part 1:

#who wins when
who_won <- lapply(mat_n, function(x) {
  mask <- matrix(FALSE, nrow = 5, ncol = 5)
  m    <- na.omit(arrayInd(match(rand_seq, x), .dim = dim(x)))
  mask[m[,]] <- TRUE
  row_sums <- rowSums(mask)
  col_sums <- colSums(mask)
  if(any(c(row_sums, col_sums) > 4)){
    
    if(any(row_sums > 4)) {
      row_mat <- x[which(row_sums > 4),,drop = FALSE]
      max_ind_row <- vector(mode = "integer", length = nrow(row_mat))
      for(i in 1:nrow(row_mat)) {
        max_ind_row[i] <- max(which(rand_seq %in% row_mat[i,])) 
      }
      max_ind_row <- min(max_ind_row)
    } else {
    max_ind_row <- NA
    }
    if(any(col_sums > 4)){
      col_mat <- x[,which(col_sums > 4), drop = FALSE]
      max_ind_col <- vector(mode = "integer", length = ncol(col_mat))
      for(i in 1:ncol(col_mat)) {
        max_ind_col[i] <- max(which(rand_seq %in% col_mat[,i])) 
      }
      max_ind_col <- min(max_ind_col)
    } else {
    max_ind_col <- NA
    } 
  min(na.omit(c(max_ind_row, max_ind_col)))
  } else {
    NA
  }
})
who_won <- unlist(who_won)

index_seq <- min(who_won, na.rm = TRUE)
last_number_drawn    <- rand_seq[[index_seq]]
bingo_card_won       <- mat_n[[which.min(who_won)]]

mask <- matrix(FALSE, nrow = 5, ncol = 5)
m    <- na.omit(arrayInd(match(rand_seq[1:index_seq], bingo_card_won ), .dim = dim(bingo_card_won )))
mask[m[,]] <- TRUE

sum_not_drawn <- sum(bingo_card_won[!mask])
(answer <- last_number_drawn * sum_not_drawn)

## [1] 44088

Part 2:

#who wins last
index_seq <- max(who_won, na.rm = TRUE)
last_number_drawn    <- rand_seq[[index_seq]]
bingo_card_won       <- mat_n[[which.max(who_won)]]

mask <- matrix(FALSE, nrow = 5, ncol = 5)
m    <- na.omit(arrayInd(match(rand_seq[1:index_seq], bingo_card_won ), .dim = dim(bingo_card_won )))
mask[m[,]] <- TRUE

sum_not_drawn <- sum(bingo_card_won[!mask])
(answer <- last_number_drawn * sum_not_drawn)

## [1] 23670

That is it. Wrapping the code into functions is advised. See you on day 5!