advent_of_code_2025

commit ce1530a4675d326b66cadabe566364326c963740
parent d2c86eae09a49a747e13e8f050b8fcbc163a44b2
Author: Eamon Caddigan <ec@eamoncaddigan.net>
Date:   Wed,  3 Dec 2025 09:57:57 -0800

Solve day 02, part 2

Diffstat:
M
src/day03.R
 | 
46
++++++++++++++++++++++++++++++++++++----------

1 file changed, 36 insertions(+), 10 deletions(-)
diff --git a/src/day03.R b/src/day03.R
@@ -16,33 +16,59 @@ parse_input <- function(input_lines) {
     lapply(as.numeric)
 }
 
-choose_batteries <- function(battery_bank) {
-  first_battery_loc <- which.max(battery_bank[1:(length(battery_bank) - 1)])
-  second_battery_loc <- first_battery_loc +
-    which.max(battery_bank[(first_battery_loc + 1):length(battery_bank)])
-  c(first_battery_loc, second_battery_loc)
+choose_batteries <- function(battery_bank, num_batteries) {
+  choose_batteries_iter <- function(batteries, bank_rema, num_batt_rema) {
+    if (num_batt_rema == 0) {
+      batteries
+    } else {
+      battery_loc <- which.max(
+        bank_rema[1:(length(bank_rema) - num_batt_rema + 1)]
+      )
+      choose_batteries_iter(
+        c(batteries, bank_rema[battery_loc]),
+        bank_rema[(battery_loc + 1):length(bank_rema)],
+        num_batt_rema - 1
+      )
+    }
+  }
+  choose_batteries_iter(NULL, battery_bank, num_batteries)
 }
 
-use_batteries <- function(battery_bank, battery_choice) {
-  battery_bank[battery_choice] |>
+use_batteries <- function(batteries) {
+  batteries |>
     paste(collapse = "") |>
     as.numeric()
 }
 
-part1 <- function(input_string) {
-  input_string |>
+solve_puzzle_for_n <- function(input_lines, n) {
+  input_lines |>
     parse_input() |>
-    (\(x) mapply(use_batteries, x, lapply(x, choose_batteries)))() |>
+    lapply(\(x) choose_batteries(x, n)) |>
+    vapply(use_batteries, numeric(1)) |>
     sum()
 }
 
+part1 <- function(input_lines) {
+  solve_puzzle_for_n(input_lines, 2)
+}
+
 test_part1 <- function() {
   stopifnot(part1(test_input) == 357)
 }
 
+part2 <- function(input_lines) {
+  solve_puzzle_for_n(input_lines, 12)
+}
+
+test_part2 <- function() {
+  stopifnot(part2(test_input) == 3121910778619)
+}
+
 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")
 }
 
 main()