1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
|
using Org.BouncyCastle.Security;
using System;
namespace Org.BouncyCastle.Pqc.Math.LinearAlgebra
{
/**
* This class implements permutations of the set {0,1,...,n-1} for some given n
* > 0, i.e., ordered sequences containing each number <tt>m</tt> (<tt>0 <=
* m < n</tt>)
* once and only once.
*/
public class Permutation
{
/**
* perm holds the elements of the permutation vector, i.e. <tt>[perm(0),
* perm(1), ..., perm(n-1)]</tt>
*/
private int[] perm;
/**
* Create the identity permutation of the given size.
*
* @param n the size of the permutation
*/
public Permutation(int n)
{
if (n <= 0)
{
throw new ArgumentException("invalid length");
}
perm = new int[n];
for (int i = n - 1; i >= 0; i--)
{
perm[i] = i;
}
}
/**
* Create a permutation using the given permutation vector.
*
* @param perm the permutation vector
*/
public Permutation(int[] perm)
{
if (!IsPermutation(perm))
{
throw new ArgumentException(
"array is not a permutation vector");
}
this.perm = IntUtils.Clone(perm);
}
/**
* Create a random permutation of the given size.
*
* @param n the size of the permutation
* @param sr the source of randomness
*/
public Permutation(int n, SecureRandom sr)
{
if (n <= 0)
{
throw new ArgumentException("invalid length");
}
perm = new int[n];
int[] help = new int[n];
for (int i = 0; i < n; i++)
{
help[i] = i;
}
int k = n;
for (int j = 0; j < n; j++)
{
int i = RandUtils.NextInt(sr, k);
k--;
perm[j] = help[i];
help[i] = help[k];
}
}
/**
* @return the permutation vector <tt>(perm(0),perm(1),...,perm(n-1))</tt>
*/
public int[] GetVector()
{
return IntUtils.Clone(perm);
}
/**
* Compute the inverse permutation <tt>P<sup>-1</sup></tt>.
*
* @return <tt>this<sup>-1</sup></tt>
*/
public Permutation ComputeInverse()
{
Permutation result = new Permutation(perm.Length);
for (int i = perm.Length - 1; i >= 0; i--)
{
result.perm[perm[i]] = i;
}
return result;
}
/**
* Compute the product of this permutation and another permutation.
*
* @param p the other permutation
* @return <tt>this * p</tt>
*/
public Permutation RightMultiply(Permutation p)
{
if (p.perm.Length != perm.Length)
{
throw new ArgumentException("length mismatch");
}
Permutation result = new Permutation(perm.Length);
for (int i = perm.Length - 1; i >= 0; i--)
{
result.perm[i] = perm[p.perm[i]];
}
return result;
}
/**
* checks if given object is equal to this permutation.
* <p>
* The method returns false whenever the given object is not permutation.
*
* @param other -
* permutation
* @return true or false
*/
public bool equals(Object other)
{
if (!(other is Permutation))
{
return false;
}
Permutation otherPerm = (Permutation)other;
return IntUtils.Equals(perm, otherPerm.perm);
}
/**
* @return a human readable form of the permutation
*/
public String ToString()
{
String result = "[" + perm[0];
for (int i = 1; i < perm.Length; i++)
{
result += ", " + perm[i];
}
result += "]";
return result;
}
/**
* Check that the given array corresponds to a permutation of the set
* <tt>{0, 1, ..., n-1}</tt>.
*
* @param perm permutation vector
* @return true if perm represents an n-permutation and false otherwise
*/
private bool IsPermutation(int[] perm)
{
int n = perm.Length;
bool[] onlyOnce = new bool[n];
for (int i = 0; i < n; i++)
{
if ((perm[i] < 0) || (perm[i] >= n) || onlyOnce[perm[i]])
{
return false;
}
onlyOnce[perm[i]] = true;
}
return true;
}
}
}
|
