From 33be068c01e20f743dd3bbe171f29ef1c8f70347 Mon Sep 17 00:00:00 2001
From: giles <giles.bradshaw@rose-ash.com>
Date: Mon, 11 May 2026 04:24:29 +0000
Subject: [PATCH] ocaml: phase 5.1 min_subarr_target.ml baseline (min subarray
 sum >= 7 = 2)

Classic two-pointer / sliding window: expand right, then shrink
left while the window still satisfies the >= constraint, recording
the smallest valid length.

  for r = 0 to n - 1 do
    sum := !sum + arr.(r);
    while !sum >= target do
      ... record (r - !l + 1) if smaller ...
      sum := !sum - arr.(!l);
      l := !l + 1
    done
  done

For [2; 3; 1; 2; 4; 3], target 7 -> window [4, 3] of length 2.

Sentinel n+1 marks "not found"; final guard reduces to 0.

Tests for + inner while shrinking loop, ref-tracked sum updated
on both expansion and contraction.

194 baseline programs total.
---
 lib/ocaml/baseline/expected.json        |  1 +
 lib/ocaml/baseline/min_subarr_target.ml | 19 +++++++++++++++++++
 plans/ocaml-on-sx.md                    |  8 ++++++++
 3 files changed, 28 insertions(+)
 create mode 100644 lib/ocaml/baseline/min_subarr_target.ml

diff --git a/lib/ocaml/baseline/expected.json b/lib/ocaml/baseline/expected.json
index 908d4325..7c10507e 100644
--- a/lib/ocaml/baseline/expected.json
+++ b/lib/ocaml/baseline/expected.json
@@ -125,6 +125,7 @@
   "merge_sort.ml": 44,
   "merge_two.ml": 441,
   "min_cost_path.ml": 12,
+  "min_subarr_target.ml": 2,
   "module_use.ml": 3,
   "monotonic.ml": 4,
   "newton_sqrt.ml": 1414,
diff --git a/lib/ocaml/baseline/min_subarr_target.ml b/lib/ocaml/baseline/min_subarr_target.ml
new file mode 100644
index 00000000..14469291
--- /dev/null
+++ b/lib/ocaml/baseline/min_subarr_target.ml
@@ -0,0 +1,19 @@
+let min_subarr_sum_at_least arr target =
+  let n = Array.length arr in
+  let best = ref (n + 1) in
+  let sum = ref 0 in
+  let l = ref 0 in
+  for r = 0 to n - 1 do
+    sum := !sum + arr.(r);
+    while !sum >= target do
+      let len = r - !l + 1 in
+      if len < !best then best := len;
+      sum := !sum - arr.(!l);
+      l := !l + 1
+    done
+  done;
+  if !best > n then 0 else !best
+
+;;
+
+min_subarr_sum_at_least [| 2; 3; 1; 2; 4; 3 |] 7
diff --git a/plans/ocaml-on-sx.md b/plans/ocaml-on-sx.md
index 1adef748..d1603223 100644
--- a/plans/ocaml-on-sx.md
+++ b/plans/ocaml-on-sx.md
@@ -407,6 +407,14 @@ _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 — min_subarr_target.ml baseline (sliding-
+  window min subarray with sum ≥ target on [2;3;1;2;4;3] target=7
+  = 2). Two-pointer: expand right, then shrink left while sum
+  stays ≥ target, recording the min length seen. Optimal window
+  is [4, 3] (positions 4-5) with sum 7, length 2. Tests `for` +
+  inner `while` shrinking loop, ref-tracked sum updated on both
+  expansion and contraction, sentinel `n + 1` for "not found".
+  194 baseline programs total.
 - 2026-05-11 Phase 5.1 — min_meeting_rooms.ml baseline (sweep-line
   for min concurrent meetings on 8 intervals = 4). Separate starts
   and ends arrays sorted independently, then a two-pointer sweep: