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  1.  
  2. let enum_cartesian_product ll =
  3. let pool = Array.map Array.of_list (Array.of_list ll) in
  4. let n = Array.length pool in
  5. let indices = Array.make n 0
  6. and lengths = Array.map (fun a -> Array.length a - 1) pool in
  7. let rec update_indices = function
  8. | i when indices.(i) <> lengths.(i) ->
  9. indices.(i) <- indices.(i) + 1
  10. | 0 -> raise BatEnum.No_more_elements
  11. | i ->
  12. indices.(i) <- 0; update_indices (i - 1)
  13. in
  14. let is_first = ref true in
  15. let next () =
  16. if !is_first then
  17. is_first := false
  18. else update_indices (n - 1);
  19. Array.to_list (BatArray.map2 Array.get pool indices)
  20. in
  21. BatEnum.from next
  24. let combinations l r =
  25. if r <= 0 then
  26. invalid_arg "r must be positive";
  27. let pool = Array.of_list l
  28. and indices = Array.init r (fun x -> x) in
  29. let n = Array.length pool in
  30. let rec next_i = function
  31. | i when indices.(i) <> i + n - r -> i
  32. | 0 -> raise BatEnum.No_more_elements
  33. | i -> next_i (i - 1)
  34. in
  35. let is_first = ref true in
  36. let next () =
  37. if !is_first then
  38. is_first := false
  39. else begin
  40. let i = next_i (r - 1) in
  41. indices.(i) <- indices.(i) + 1;
  42. for j = i + 1 to r - 1 do indices.(j) <- indices.(j - 1) + 1 done
  43. end;
  44. map (Array.get pool) (Array.to_list indices)
  45. in
  46. BatEnum.from next
  47.  
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