ocaml: phase 5.1 subset_sum.ml baseline (count subsets of [1..8] summing to 10 = 8)

Pure recursion — at each element, take it or don't:

  let rec count_subsets xs target =
    match xs with
    | [] -> if target = 0 then 1 else 0
    | x :: rest ->
      count_subsets rest target
      + count_subsets rest (target - x)

For [1;2;3;4;5;6;7;8] target 10, the recursion tree has 2^8 = 256
leaves. Returns 8 — number of subsets summing to 10:

  1+2+3+4, 1+2+7, 1+3+6, 1+4+5, 2+3+5, 2+8, 3+7, 4+6 = 8

Tests doubly-recursive list traversal pattern with single-arg list
+ accumulator-via-target.

65 baseline programs total.

lib/ocaml/baseline/expected.json

@@ -57,6 +57,7 @@
   "run_length.ml": 11,
   "safe_div.ml": 20,
   "shuffle.ml": 55,
+  "subset_sum.ml": 8,
   "word_freq.ml": 8,
   "zip_unzip.ml": 1000,
   "sieve.ml": 15,

lib/ocaml/baseline/subset_sum.ml

@@ -0,0 +1,10 @@
+let rec count_subsets xs target =
+  match xs with
+  | [] -> if target = 0 then 1 else 0
+  | x :: rest ->
+    count_subsets rest target
+    + count_subsets rest (target - x)
+
+;;
+
+count_subsets [1; 2; 3; 4; 5; 6; 7; 8] 10