advent_of_code_2025

commit 62b2eb241aab95b8e6e7047deb18ed1214cde74f
parent e32ec9ee60192eb5a49b48830318adfaedf58cd3
Author: Eamon Caddigan <ec@eamoncaddigan.net>
Date:   Sat,  6 Dec 2025 21:07:40 -0800

Solve day 06, part 2

Diffstat:
M
src/day06.R
 | 
31
+++++++++++++++++++++++++++++++

1 file changed, 31 insertions(+), 0 deletions(-)
diff --git a/src/day06.R b/src/day06.R
@@ -40,9 +40,40 @@ test_part1 <- function() {
   stopifnot(part1(test_input) == 4277556)
 }
 
+
+parse_part2 <- function(input_lines) {
+  char_mat <- input_lines |>
+    strsplit("", fixed = TRUE) |>
+    (\(x) matrix(unlist(x), ncol = length(x), byrow = FALSE))()
+  is_separator <- apply(char_mat == " ", 1, all)
+  list(
+    numbers = char_mat[!is_separator, 1:(ncol(char_mat) - 1)] |>
+      apply(1, \(x) paste(x, collapse = "")) |>
+      as.numeric() |>
+      split(cumsum(is_separator)[!is_separator]),
+    operators = char_mat[char_mat[, ncol(char_mat)] != " ", ncol(char_mat)]
+  )
+}
+
+part2 <- function(input_lines) {
+  input_parsed <- parse_part2(input_lines)
+  mapply(
+    \(x, y) if (y == "+") sum(x) else prod(x),
+    input_parsed$numbers,
+    input_parsed$operators
+  ) |>
+    sum()
+}
+
+test_part2 <- function() {
+  stopifnot(part2(test_input) == 3263827)
+}
+
 main <- function() {
   test_part1()
   cat(sprintf("Part 1 solution: %0.0f\n", part1(puzzle_input)))
+  test_part2()
+  cat(sprintf("Part 2 solution: %0.0f\n", part2(puzzle_input)))
 }
 
 main()