2021 Day 5

Author

Nathan Moore

— Day 5: Hydrothermal Venture —

You come across a field of hydrothermal vents.

Consider only horizontal and vertical lines. At how many points do at least two lines overlap?

library(tidyverse)

my_file <- here::here("2021", "data-2021-05.txt")
x <- readLines(my_file)

function

create_plumes <- function(x) {
  tibble(init = x) %>%
    separate(init, c("x1y1", "x2y2"), sep = " ->") %>%
    separate(x1y1, c("x1", "y1"), sep = ",", convert = TRUE) %>%
    separate(x2y2, c("x2", "y2"), sep = ",", convert = TRUE) %>%
    mutate(vert = x1 == x2,
           hori = y1 == y2)
}

Do the thing

plumes = create_plumes(x)

# range from 10 to 990
sea_floor = array(0, c(1000,1000))

for (j in 1:nrow(plumes)) {
    if (plumes$vert[[j]] | plumes$hori[[j]]) {

        sea_floor[plumes$x1[[j]]:plumes$x2[[j]], plumes$y1[[j]]:plumes$y2[[j]]] = 1 + sea_floor[plumes$x1[[j]]:plumes$x2[[j]], plumes$y1[[j]]:plumes$y2[[j]]]
    }
}

# part one answer
sum(sea_floor > 1)

[1] 6311

— Part Two —

Actually, we need to consider diagonals as well.

Consider all of the lines. At how many points do at least two lines overlap?

plumes = create_plumes(x)

sea_floor = array(0, c(1000,1000))

for (j in 1:nrow(plumes)) {
    # sequences for x and y
    xx = seq(plumes$x1[[j]], plumes$x2[[j]])
    yy = seq(plumes$y1[[j]], plumes$y2[[j]])
    # adjust for vert or horizontal
    if (length(xx) == 1) xx = rep(xx, length(yy))
    if (length(yy) == 1) yy = rep(yy, length(xx))
    # loop for sea floor positions
    for (k in seq_len(max(length(xx), length(yy)))) {
        sea_floor[xx[k], yy[k]] = sea_floor[xx[k], yy[k]] + 1
    }
}

# part two answer
sum(sea_floor > 1)

[1] 19929