advent_of_code_2025

commit 9b44bf6e9f09fa23967bd471e421b2355c2ed340
parent 98b333587165f6f2b97b5d74e40ed9d36132d43c
Author: Eamon Caddigan <ec@eamoncaddigan.net>
Date:   Thu,  4 Dec 2025 12:57:38 -0800

Solve day 03, part 2

Diffstat:
M
src/day04.R
 | 
38
++++++++++++++++++++++++++++++++------

1 file changed, 32 insertions(+), 6 deletions(-)
diff --git a/src/day04.R b/src/day04.R
@@ -43,22 +43,48 @@ count_neighbors <- function(diagram) {
   neighbors
 }
 
+mark_moveable <- function(diagram) {
+  (diagram == "@") & (count_neighbors(diagram) < 4)
+}
+
 part1 <- function(input_lines) {
-  diagram <- parse_input(input_lines)
-  neighbors <- count_neighbors(diagram)
-  is_movable <- (diagram == "@") & (neighbors < 4)
-  sum(is_movable)
+  input_lines |>
+    parse_input() |>
+    mark_moveable() |>
+    sum()
 }
 
 test_part1 <- function() {
   stopifnot(part1(test_input) == 13)
 }
 
+count_moveable <- function(diagram) {
+  total_moved <- 0
+  repeat {
+    moveable <- mark_moveable(diagram)
+    moveable_count <- sum(moveable)
+    if (moveable_count == 0) break
+    total_moved <- total_moved + moveable_count
+    diagram[moveable] <- "."
+  }
+  total_moved
+}
+
+part2 <- function(input_lines) {
+  input_lines |>
+    parse_input() |>
+    count_moveable()
+}
+
+test_part2 <- function() {
+  stopifnot(part2(test_input) == 43)
+}
+
 main <- function() {
   test_part1()
   cat("Part 1 solution: ", part1(puzzle_input), "\n")
-  # test_part2()
-  # cat("Part 2 solution: ", sprintf("%0.0f", part2(puzzle_input)), "\n")
+  test_part2()
+  cat("Part 2 solution: ", part2(puzzle_input), "\n")
 }
 
 main()