Created
December 9, 2025 08:45
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| library(tidyverse) | |
| library(sf) | |
| input <- readr::read_lines("inputs/actual/09.txt") | |
| points <- str_split(input, ",") |> | |
| lapply(as.integer) | |
| make_rectangle <- function(p1, p2) { | |
| sf::st_polygon(list(rbind( | |
| c(p1[1], p1[2]), | |
| c(p2[1], p1[2]), | |
| c(p2[1], p2[2]), | |
| c(p1[1], p2[2]), | |
| c(p1[1], p1[2]) | |
| ))) | |
| } | |
| make_boundary <- function(points) { | |
| sf::st_polygon(list(matrix(flatten_int(c(points, points[1])), ncol = 2, byrow = TRUE))) | |
| } | |
| make_all_rectangles <- function(points) { | |
| map( | |
| points, | |
| \(p) { | |
| map( | |
| points, | |
| \(q) { | |
| if (p[[1]] < q[[1]] || p[[2]] < q[[2]]) { | |
| make_rectangle(p, q) | |
| } | |
| } | |
| ) | |
| } | |
| ) |> | |
| flatten() |> | |
| discard(is.null) | |
| } | |
| bounds <- make_boundary(points) | |
| rs <- make_all_rectangles(points) | |
| rs_sf <- sf::st_as_sf(sf::st_sfc(rs)) | |
| valid <- st_filter(rs_sf, bounds, .predicate = sf::st_within) | |
| area <- function(geom) { | |
| bbox <- sf::st_bbox(geom) | |
| x <- 1 + abs(bbox$xmin - bbox$xmax) | |
| y <- 1 + abs(bbox$ymin - bbox$ymax) | |
| unname(x * y) | |
| } | |
| max(sapply(valid$x, area)) |
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