46 lines
1.7 KiB
Text
46 lines
1.7 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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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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def qpartition (as : Array α) (lt : α → α → Bool) (lo hi : Nat) : Nat × Array α :=
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if h : as.size = 0 then (0, as) else have : Inhabited α := ⟨as[0]'(by revert h; cases as.size <;> simp [Nat.zero_lt_succ])⟩ -- TODO: remove
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let mid := (lo + hi) / 2
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let as := if lt (as.get! mid) (as.get! lo) then as.swap! lo mid else as
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let as := if lt (as.get! hi) (as.get! lo) then as.swap! lo hi else as
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let as := if lt (as.get! mid) (as.get! hi) then as.swap! mid hi else as
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let pivot := as.get! hi
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let rec loop (as : Array α) (i j : Nat) :=
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if h : j < hi then
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if lt (as.get! j) pivot then
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let as := as.swap! i j
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loop as (i+1) (j+1)
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else
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loop as i (j+1)
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else
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let as := as.swap! i hi
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(i, as)
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loop as lo lo
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termination_by _ => hi - j
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@[inline] partial def qsort (as : Array α) (lt : α → α → Bool) (low := 0) (high := as.size - 1) : Array α :=
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let rec @[specialize] sort (as : Array α) (low high : Nat) :=
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if low < high then
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let p := qpartition as lt low high;
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-- TODO: fix `partial` support in the equation compiler, it breaks if we use `let (mid, as) := partition as lt low high`
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let mid := p.1
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let as := p.2
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if mid >= high then as
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else
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let as := sort as low mid
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sort as (mid+1) high
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else as
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sort as low high
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end Array
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