day 12 tweaks

2 files changed, 38 insertions, 9 deletions

diff --git a/aoc2023-other/day-12/day-12.rkt b/aoc2023-other/day-12/day-12.rkt
index f7d303c..d07994f 100644
--- a/aoc2023-other/day-12/day-12.rkt
+++ b/aoc2023-other/day-12/day-12.rkt
@@ -16,22 +16,24 @@
  (do-count template spring-group left-in-group need-gap?)
  ;; template: list of spring positions
  ;; spring-group: list of remaining contiguous groups of damaged springs
- ;; left-in-group: springs remaining in current spring group being placed
- ;; need-gap?: did we just finish placing a spring group
+ ;; left-in-group: springs remaining in current bad spring group being placed
+ ;; need-gap?: did we just finish placing a bad spring group
  ;;            and need at least one undamaged spring before starting the next one?
  (match (list template spring-group left-in-group need-gap?)
-   ;; no gears left to place, this is an OK arrangement, count it
+   ;; no springs left to place and no places left to place springs
+   ;; this is an OK arrangement, count it
    [(list '() '() 0 _) 1]
-   ;; ambiguous wildcard, try both skipping this spot and starting a gear group here
+   ;; ambiguous wildcard, try both skipping this spot and starting a damaged spring group here
    [(list (list* #\? t-rest) (list* g g-rest) 0 #f)
     (+ (do-count t-rest g-rest (sub1 g) (= g 1)) (do-count t-rest spring-group 0 #f))]
-   ;; definitely a place for a good spring (.); move on without consuming any spring groups
-   [(or (list (list* #\? t-rest) '() 0 #f)
-        (list (list* #\? t-rest) _ 0 #t)
-        (list (list* #\. t-rest) _ 0 _))
+   ;; definitely a place for a good spring (.), move on without consuming any spring groups
+   [(or (list (list* #\? t-rest) '() 0 #f) ; good spring, no more damaged springs to place
+        (list (list* #\? t-rest) _ 0 #t) ; good spring right after finishing a group of bad springs
+        (list (list* #\. t-rest) _ 0 _)) ; known good spring
     (do-count t-rest spring-group 0 #f)]
-   ;; definitely a place for a damaged spring (#); use the next spring group and remove 1 from it
+   ;; start of bad spring (#) group, use the next spring group and remove 1 from it
    [(list (list* #\# t-rest) (list* g g-rest) 0 #f) (do-count t-rest g-rest (sub1 g) (= g 1))]
+   ;; continuation of bad spring group, same
    [(list (list* (or #\? #\#) t-rest) g left #f) (do-count t-rest g (sub1 left) (= left 1))]
    ;; if nothing above works, this arrangement's invalid
    [_ 0]))
diff --git a/aoc2023/src/utilities/array2d.gleam b/aoc2023/src/utilities/array2d.gleam
new file mode 100644
index 0000000..1ad824c
--- /dev/null
+++ b/aoc2023/src/utilities/array2d.gleam
@@ -0,0 +1,27 @@
+import gleam/list
+import gleam/dict.{type Dict}
+import gleam/string
+
+pub type Posn {
+  Posn(x: Int, y: Int)
+}
+
+pub type Array2D(a) =
+  Dict(Posn, a)
+
+pub fn to_2d_array(xss: List(List(a))) -> Array2D(a) {
+  {
+    use x, row <- list.index_map(xss)
+    use y, cell <- list.index_map(row)
+    #(Posn(x, y), cell)
+  }
+  |> list.flatten
+  |> dict.from_list
+}
+
+pub fn parse_grid(str: String) -> Array2D(String) {
+  str
+  |> string.split("\n")
+  |> list.map(string.to_graphemes)
+  |> to_2d_array
+}