giles
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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.
11 lines
220 B
OCaml
11 lines
220 B
OCaml
let rec count_subsets xs target =
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match xs with
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| [] -> if target = 0 then 1 else 0
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| x :: rest ->
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count_subsets rest target
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+ count_subsets rest (target - x)
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;;
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count_subsets [1; 2; 3; 4; 5; 6; 7; 8] 10
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