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December 21, 2023 03:31
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2023 advent of code day 15
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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) |
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