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