32 lines
1.2 KiB
Text
32 lines
1.2 KiB
Text
/-
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Copyright (c) 2019 Microsoft Corporation. All rights reserved.
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Released under Apache 2.0 license as described in the file LICENSE.
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Authors: Leonardo de Moura
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-/
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prelude
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import init.data.array.basic
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universes u v
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namespace Array
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-- TODO: remove the [Inhabited α] parameters as soon as we have the tactic framework for automating proof generation and using Array.fget
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-- TODO: remove `partial` using well-founded recursion
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@[specialize] partial def binSearchAux {α : Type u} {β : Type v} [Inhabited α] [Inhabited β] (lt : α → α → Bool) (found : Option α → β) (as : Array α) (k : α) : Nat → Nat → β
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| lo, hi =>
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if lo <= hi then
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let m := (lo + hi)/2;
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let a := as.get! m;
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if lt a k then binSearchAux (m+1) hi
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else if lt k a then
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if m == 0 then found none
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else binSearchAux lo (m-1)
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else found (some a)
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else found none
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@[inline] def binSearch {α : Type} [Inhabited α] (as : Array α) (k : α) (lt : α → α → Bool) (lo := 0) (hi := as.size - 1) : Option α :=
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binSearchAux lt id as k lo hi
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@[inline] def binSearchContains {α : Type} [Inhabited α] (as : Array α) (k : α) (lt : α → α → Bool) (lo := 0) (hi := as.size - 1) : Bool :=
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binSearchAux lt Option.isSome as k lo hi
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end Array
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