From 2726ed9b8ab99118872d58524a40ca87757b4705 Mon Sep 17 00:00:00 2001
From: giles <giles.bradshaw@rose-ash.com>
Date: Mon, 11 May 2026 02:14:44 +0000
Subject: [PATCH] ocaml: phase 5.1 palindrome_part.ml baseline (min cuts
 "aabba" = 1)

Two-phase palindrome-partition DP for the minimum-cuts variant:

  Phase 1: is_pal[i][j] palindrome table via length-major fill
           (single chars, then pairs, then expand inward).

  Phase 2: cuts[i] = 0 if s[0..i] is itself a palindrome,
                  = min over j of (cuts[j-1] + 1)
                    where s[j..i] is a palindrome.

  min_cut "aabba" = 1   ("a" | "abba")

Tests two sequential 2D DPs sharing the same is_pal matrix,
inline begin/end branches inside the length-major fill, mixed
bool and int 2D arrays.

181 baseline programs total.
---
 lib/ocaml/baseline/expected.json      |  1 +
 lib/ocaml/baseline/palindrome_part.ml | 35 +++++++++++++++++++++++++++
 plans/ocaml-on-sx.md                  | 10 ++++++++
 3 files changed, 46 insertions(+)
 create mode 100644 lib/ocaml/baseline/palindrome_part.ml

diff --git a/lib/ocaml/baseline/expected.json b/lib/ocaml/baseline/expected.json
index 8561668a..35371c95 100644
--- a/lib/ocaml/baseline/expected.json
+++ b/lib/ocaml/baseline/expected.json
@@ -125,6 +125,7 @@
   "mutable_record.ml": 10,
   "option_match.ml": 5,
   "palindrome.ml": 4,
+  "palindrome_part.ml": 1,
   "palindrome_sum.ml": 49500,
   "paren_depth.ml": 7,
   "partition.ml": 3025,
diff --git a/lib/ocaml/baseline/palindrome_part.ml b/lib/ocaml/baseline/palindrome_part.ml
new file mode 100644
index 00000000..0f4b7fb8
--- /dev/null
+++ b/lib/ocaml/baseline/palindrome_part.ml
@@ -0,0 +1,35 @@
+let min_cut s =
+  let n = String.length s in
+  if n <= 1 then 0
+  else begin
+    let is_pal = Array.init n (fun _ -> Array.make n false) in
+    for i = 0 to n - 1 do is_pal.(i).(i) <- true done;
+    for len = 2 to n do
+      for i = 0 to n - len do
+        let j = i + len - 1 in
+        if s.[i] = s.[j] then begin
+          if len = 2 then is_pal.(i).(j) <- true
+          else is_pal.(i).(j) <- is_pal.(i + 1).(j - 1)
+        end
+      done
+    done;
+    let cuts = Array.make n 0 in
+    for i = 0 to n - 1 do
+      if is_pal.(0).(i) then cuts.(i) <- 0
+      else begin
+        let best = ref i in
+        for j = 1 to i do
+          if is_pal.(j).(i) then begin
+            let c = cuts.(j - 1) + 1 in
+            if c < !best then best := c
+          end
+        done;
+        cuts.(i) <- !best
+      end
+    done;
+    cuts.(n - 1)
+  end
+
+;;
+
+min_cut "aabba"
diff --git a/plans/ocaml-on-sx.md b/plans/ocaml-on-sx.md
index f21989ca..6cc60e48 100644
--- a/plans/ocaml-on-sx.md
+++ b/plans/ocaml-on-sx.md
@@ -407,6 +407,16 @@ _Newest first._
   binary search tree (`type 'a tree = Leaf | Node of 'a * 'a tree *
   'a tree`) with insert + in-order traversal. Tests parametric ADT,
   recursive match, List.append, List.fold_left.
+- 2026-05-11 Phase 5.1 — palindrome_part.ml baseline (minimum
+  palindrome-partition cuts in "aabba" = 1). Two-phase DP:
+    1) `is_pal.(i).(j)` table via length-major iteration.
+    2) `cuts.(i)` = min cuts for prefix s[0..i]; if s[0..i] itself
+       is a palindrome, 0; else min over j of (cuts.(j-1) + 1)
+       where s[j..i] is a palindrome.
+  For "aabba" the optimal partition is "a" | "abba" = 1 cut.
+  Tests sequential 2D DP passes sharing the same `is_pal` matrix,
+  inline `if/else begin/end` blocks under length-major fill, mixed
+  bool and int 2D arrays. 181 baseline programs total.
 - 2026-05-11 Phase 5.1 — island_count.ml baseline (count 4-connected
   components of 1-cells in a 6×7 grid = 5). DFS flood from every
   unvisited 1-cell. Counted islands: