40 lines
1009 B
Go
40 lines
1009 B
Go
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// Copyright (c) 2014 The mathutil Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package mathutil // import "modernc.org/mathutil"
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import (
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"sort"
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)
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// PermutationFirst generates the first permutation of data.
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func PermutationFirst(data sort.Interface) {
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sort.Sort(data)
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}
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// PermutationNext generates the next permutation of data if possible and
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// return true. Return false if there is no more permutation left. Based on
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// the algorithm described here:
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// http://en.wikipedia.org/wiki/Permutation#Generation_in_lexicographic_order
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func PermutationNext(data sort.Interface) bool {
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var k, l int
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for k = data.Len() - 2; ; k-- { // 1.
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if k < 0 {
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return false
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}
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if data.Less(k, k+1) {
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break
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}
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}
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for l = data.Len() - 1; !data.Less(k, l); l-- { // 2.
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}
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data.Swap(k, l) // 3.
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for i, j := k+1, data.Len()-1; i < j; i++ { // 4.
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data.Swap(i, j)
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j--
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}
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return true
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}
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