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Recursive 4-arm match on (a, b) tuples threading a carry: match (a, b) with | ([], []) -> if carry = 0 then [] else [carry] | (x :: xs, []) -> (s mod 10) :: aux xs [] (s / 10) where s = x + carry | ([], y :: ys) -> ... | (x :: xs, y :: ys) -> ... where s = x + y + carry Little-endian digit lists. Three tests: [9;9;9] + [1] = [0;0;0;1] (=1000, digit sum 1) [5;6;7] + [8;9;1] = [3;6;9] (=963, digit sum 18) [9;9;9;9;9;9;9;9] + [1] length 9 (carry propagates 8x) Sum = 1 + 18 + 9 = 28. Exercises tuple-pattern match on nested list-cons with the integer arithmetic and carry-threading idiom typical of multi-precision implementations. 52 baseline programs total.
25 lines
609 B
OCaml
25 lines
609 B
OCaml
let bigint_add a b =
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let rec aux a b carry =
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match (a, b) with
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| ([], []) -> if carry = 0 then [] else [carry]
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| (x :: xs, []) ->
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let s = x + carry in
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(s mod 10) :: aux xs [] (s / 10)
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| ([], y :: ys) ->
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let s = y + carry in
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(s mod 10) :: aux [] ys (s / 10)
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| (x :: xs, y :: ys) ->
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let s = x + y + carry in
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(s mod 10) :: aux xs ys (s / 10)
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in
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aux a b 0
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;;
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let r1 = bigint_add [9;9;9] [1] in
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let r2 = bigint_add [5;6;7] [8;9;1] in
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let r3 = bigint_add [9;9;9;9;9;9;9;9] [1] in
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List.fold_left (+) 0 r1
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+ List.fold_left (+) 0 r2
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+ List.length r3
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