github.com/cznic/mathutil@v0.0.0-20181122101859-297441e03548/permute.go (about)

     1  // Copyright (c) 2014 The mathutil Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package mathutil
     6  
     7  import (
     8  	"sort"
     9  )
    10  
    11  // PermutationFirst generates the first permutation of data.
    12  func PermutationFirst(data sort.Interface) {
    13  	sort.Sort(data)
    14  }
    15  
    16  // PermutationNext generates the next permutation of data if possible and
    17  // return true.  Return false if there is no more permutation left.  Based on
    18  // the algorithm described here:
    19  // http://en.wikipedia.org/wiki/Permutation#Generation_in_lexicographic_order
    20  func PermutationNext(data sort.Interface) bool {
    21  	var k, l int
    22  	for k = data.Len() - 2; ; k-- { // 1.
    23  		if k < 0 {
    24  			return false
    25  		}
    26  
    27  		if data.Less(k, k+1) {
    28  			break
    29  		}
    30  	}
    31  	for l = data.Len() - 1; !data.Less(k, l); l-- { // 2.
    32  	}
    33  	data.Swap(k, l)                             // 3.
    34  	for i, j := k+1, data.Len()-1; i < j; i++ { // 4.
    35  		data.Swap(i, j)
    36  		j--
    37  	}
    38  	return true
    39  }