1 files changed, 77 insertions, 0 deletions
diff --git a/ocaml/lib/year2025/day03/part02/battery_bank.ml b/ocaml/lib/year2025/day03/part02/battery_bank.ml
new file mode 100644
index 0000000..d7dc213
--- /dev/null
+++ b/ocaml/lib/year2025/day03/part02/battery_bank.ml
@@ -0,0 +1,77 @@
+open Battery
+
+module BatteryBank = struct
+  type t = Battery.t list
+
+  type highest = {one: Battery.t option; two: Battery.t option}
+
+  let rec highest_joltage bb =
+    assert (List.length bb > 0) ;
+    match highest_joltage_aux {one= None; two= None} bb with
+    | {one= None; two= None} ->
+        0
+    | {one= Some x; two= Some y} ->
+        int_of_string (Battery.to_string x ^ Battery.to_string y)
+    | _ ->
+        failwith "highest_joltage must be two digits"
+
+  and highest_joltage_aux acc = function
+    | [] ->
+        acc
+    | [elt] -> (
+      match acc with
+      | {one= None; two= None} ->
+          {one= Some (Battery.of_int 0); two= Some elt}
+      | {one= Some first; two= None} ->
+          {one= Some first; two= Some elt}
+      | {one= None; two= Some second} ->
+          {one= Some second; two= Some elt}
+      | {one= Some first; two= Some second} ->
+          if elt > second then {one= Some first; two= Some elt}
+          else {one= Some first; two= Some second} )
+    | h :: t ->
+        highest_joltage_aux
+          ( match acc with
+          | {one= None; two= None} ->
+              {one= Some h; two= None}
+          | {one= Some first; two= None} ->
+              let second = Battery.of_int 0 in
+              swap_if_higher first second h
+          | {one= Some first; two= Some second} ->
+              swap_if_higher first second h
+          | _ ->
+              failwith "this branch should be impossible" )
+          t
+
+  and swap_if_higher first second considering =
+    assert (first >= second) ;
+    let c_gt_f = Battery.compare considering first = 1 in
+    let c_gt_s = Battery.compare considering second = 1 in
+    match (c_gt_f, c_gt_s) with
+    | true, true ->
+        {one= Some considering; two= None}
+    | false, true ->
+        {one= Some first; two= Some considering}
+    | true, false ->
+        failwith "[second] should never be greater than [first]"
+    | false, false ->
+        {one= Some first; two= Some second}
+
+  let of_string s =
+    s |> String.to_seq
+    |> Seq.map (fun c -> Char.escaped c |> int_of_string |> Battery.of_int)
+    |> List.of_seq
+
+  let of_list lst = lst
+
+  let to_list bb = bb
+
+  let pp bb =
+    "[ "
+    ^ ( bb |> List.map Battery.pp
+      |> List.fold_left
+           (fun acc b ->
+             if acc = "" then b ^ ";" else Printf.sprintf "%s %s;" acc b )
+           "" )
+    ^ " ]"
+end