2023 advent of code day 15

day_15.R

input <- data.frame("label" = t(read.table("input.txt", sep = ",")))
input$row <- seq_along(input[,1])

hasher <- function(x){
  current <- 0L
  for(i in 1:length(x)){
    current <- ((current + utf8ToInt(x[i])) * 17L) %% 256L
  } 
  return(current)
}

input$hash <- sapply(strsplit(input$label, ""), hasher)

sum(input$hash)

#second star
input$length <- sapply(input$label, function(x){as.integer(gsub("[^0-9]", "", x))})
input$label <- sapply(input$label, function(x){gsub("[0-9=-]", "", x)})
input$hash <- sapply(strsplit(input$label, ""), hasher)
# remove lenses up through last "-" in lens group
input$label_id <- with(input, ave(seq_along(label), label, FUN = seq_along))
input <- do.call(rbind, by(input, input$label, function(x)
  {transform(x, max_na = ifelse(any(is.na(length)), max(which(is.na(length))), 0))
  }))
input <- input[input$label_id > input$max_na, ]
input$hash <- input$hash+1
input <- input[order(input$row), ]
input <- do.call(rbind, lapply(split(input, list(input$label, input$hash)), tail, 1L)) # replace lenses already in boxes

input$slot <- with(input, ave(seq_along(hash), hash, FUN = seq_along))

input$focus <- Reduce(`*`, input[c(3,4,7)])

sum(input$focus)