59 lines
1.1 KiB
OCaml
59 lines
1.1 KiB
OCaml
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exception Empty
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type 'a queue_cell =
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Nil
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| Cons of 'a * 'a queue_cell ref
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type 'a t =
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{ mutable head: 'a queue_cell;
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mutable tail: 'a queue_cell }
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let new () =
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{ head = Nil; tail = Nil }
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let clear q =
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q.head <- Nil; q.tail <- Nil
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let add x q =
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match q.tail with
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Nil -> (* if tail = Nil then head = Nil *)
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let c = Cons(x, ref Nil) in
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q.head <- c; q.tail <- c
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| Cons(_, newtailref) ->
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let c = Cons(x, ref Nil) in
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newtailref := c;
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q.tail <- c
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let peek q =
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match q.head with
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Nil ->
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raise Empty
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| Cons(x, _) ->
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x
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let take q =
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match q.head with
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Nil ->
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raise Empty
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| Cons(x, rest) ->
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q.head <- !rest;
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begin match !rest with
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Nil -> q.tail <- Nil
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| _ -> ()
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end;
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x
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let rec length_aux = function
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Nil -> 0
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| Cons(_, rest) -> succ (length_aux !rest)
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let length q = length_aux q.head
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let rec iter_aux f = function
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Nil ->
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()
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| Cons(x, rest) ->
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f x; iter_aux f !rest
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let iter f q = iter_aux f q.head
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