From aee7226b9c65009c48b0d100c8b682ac651ebc48 Mon Sep 17 00:00:00 2001
From: giles <giles.bradshaw@rose-ash.com>
Date: Sat, 9 May 2026 10:21:11 +0000
Subject: [PATCH] ocaml: phase 5.1 coin_change.ml baseline (DP, 67c with
 [1;5;10;25] = 6 coins)
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Bottom-up dynamic programming. dp[i] = minimum coins to make
amount i.

  let dp = Array.make (target + 1) (target + 1) in   (* sentinel *)
  dp.(0) <- 0;
  for i = 1 to target do
    List.iter (fun c ->
      if c <= i && dp.(i - c) + 1 < dp.(i) then
        dp.(i) <- dp.(i - c) + 1
    ) coins
  done

Sentinel 'target + 1' means impossible — any real solution uses at
most 'target' coins.

  coin_change [1; 5; 10; 25] 67   = 6   (= 25+25+10+5+1+1)

Exercises Array.make + arr.(i) + arr.(i) <- v + nested
for/List.iter + guard 'c <= i'.

47 baseline programs total.
---
 lib/ocaml/baseline/coin_change.ml | 15 +++++++++++++++
 lib/ocaml/baseline/expected.json  |  1 +
 plans/ocaml-on-sx.md              |  8 ++++++++
 3 files changed, 24 insertions(+)
 create mode 100644 lib/ocaml/baseline/coin_change.ml

diff --git a/lib/ocaml/baseline/coin_change.ml b/lib/ocaml/baseline/coin_change.ml
new file mode 100644
index 00000000..5743a879
--- /dev/null
+++ b/lib/ocaml/baseline/coin_change.ml
@@ -0,0 +1,15 @@
+let coin_change coins target =
+  let dp = Array.make (target + 1) (target + 1) in
+  dp.(0) <- 0;
+  for i = 1 to target do
+    List.iter (fun c ->
+      if c <= i && dp.(i - c) + 1 < dp.(i) then
+        dp.(i) <- dp.(i - c) + 1
+    ) coins
+  done;
+  if dp.(target) > target then -1
+  else dp.(target)
+
+;;
+
+coin_change [1; 5; 10; 25] 67
diff --git a/lib/ocaml/baseline/expected.json b/lib/ocaml/baseline/expected.json
index 5e4f9195..6e0e9145 100644
--- a/lib/ocaml/baseline/expected.json
+++ b/lib/ocaml/baseline/expected.json
@@ -10,6 +10,7 @@
   "caesar.ml": 215,
   "calc.ml": 13,
   "closures.ml": 315,
+  "coin_change.ml": 6,
   "csv.ml": 10,
   "exception_handle.ml": 4,
   "expr_eval.ml": 16,
diff --git a/plans/ocaml-on-sx.md b/plans/ocaml-on-sx.md
index aabe7b2e..0d6bb898 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.
+- 2026-05-09 Phase 5.1 — coin_change.ml baseline (min coin DP, 67¢
+  with [1;5;10;25] → 6 coins). Bottom-up DP: `dp[i]` = min coins
+  for amount i. For each amount 1..target, iterate coins and
+  relax `dp[i] = min(dp[i], dp[i-c] + 1)`. Sentinel `target + 1`
+  represents "impossible" since any real solution uses at most
+  target coins. 67 = 25+25+10+5+1+1 = 6 coins. Exercises
+  Array.make + arr.(i) + arr.(i) <- v + nested for/List.iter +
+  guard `c <= i`. 47 baseline programs total.
 - 2026-05-09 Phase 5.1 — kadane.ml baseline (Kadane's max subarray
   sum = 6). Classic O(n) algorithm using two refs and `max`. For
   [-2;1;-3;4;-1;2;1;-5;4] the optimal subarray is [4;-1;2;1] = 6.