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
|
<HTML>
<!--
-- Copyright (c) 1996-1999
-- Silicon Graphics Computer Systems, Inc.
--
-- Permission to use, copy, modify, distribute and sell this software
-- and its documentation for any purpose is hereby granted without fee,
-- provided that the above copyright notice appears in all copies and
-- that both that copyright notice and this permission notice appear
-- in supporting documentation. Silicon Graphics makes no
-- representations about the suitability of this software for any
-- purpose. It is provided "as is" without express or implied warranty.
--
-- Copyright (c) 1994
-- Hewlett-Packard Company
--
-- Permission to use, copy, modify, distribute and sell this software
-- and its documentation for any purpose is hereby granted without fee,
-- provided that the above copyright notice appears in all copies and
-- that both that copyright notice and this permission notice appear
-- in supporting documentation. Hewlett-Packard Company makes no
-- representations about the suitability of this software for any
-- purpose. It is provided "as is" without express or implied warranty.
--
-->
<Head>
<Title>random_shuffle</Title>
<!-- Generated by htmldoc -->
</HEAD>
<BODY BGCOLOR="#ffffff" LINK="#0000ee" TEXT="#000000" VLINK="#551a8b"
ALINK="#ff0000">
<IMG SRC="CorpID.gif"
ALT="SGI" HEIGHT="43" WIDTH="151">
<!--end header-->
<BR Clear>
<H1>random_shuffle</H1>
<Table CellPadding=0 CellSpacing=0 width=100%>
<TR>
<TD Align=left><Img src = "algorithms.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD>
<TD Align=right><Img src = "function.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD>
</TR>
<TR>
<TD Align=left VAlign=top><b>Category</b>: algorithms</TD>
<TD Align=right VAlign=top><b>Component type</b>: function</TD>
</TR>
</Table>
<h3>Prototype</h3>
<tt>Random_shuffle</tt> is an overloaded name; there are actually two
<tt>random_shuffle</tt> functions.
<pre>
template <class <A href="RandomAccessIterator.html">RandomAccessIterator</A>>
void random_shuffle(RandomAccessIterator first, RandomAccessIterator last);
template <class <A href="RandomAccessIterator.html">RandomAccessIterator</A>, class <A href="RandomNumberGenerator.html">RandomNumberGenerator</A>>
void random_shuffle(RandomAccessIterator first, RandomAccessIterator last,
RandomNumberGenerator& rand)
</pre>
<h3>Description</h3>
<tt>Random_shuffle</tt> randomly rearranges the elements in the range
<tt>[first, last)</tt>: that is, it randomly picks one of the <tt>N!</tt> possible
orderings, where <tt>N</tt> is <tt>last - first</tt>. <A href="#1">[1]</A> There are two different
versions of <tt>random_shuffle</tt>. The first version uses an internal random
number generator, and the second uses a <A href="RandomNumberGenerator.html">Random Number Generator</A>,
a special kind of <A href="functors.html">function object</A>, that is explicitly passed as
an argument.
<h3>Definition</h3>
Defined in the standard header <A href="algorithm">algorithm</A>, and in the nonstandard
backward-compatibility header <A href="algo.h">algo.h</A>.
<h3>Requirements on types</h3>
For the first version:
<UL>
<LI>
<tt>RandomAccessIterator</tt> is a model of <A href="RandomAccessIterator.html">Random Access Iterator</A>
</UL>
For the second version:
<UL>
<LI>
<tt>RandomAccessIterator</tt> is a model of <A href="RandomAccessIterator.html">Random Access Iterator</A>
<LI>
<tt>RandomNumberGenerator</tt> is a model of <A href="RandomNumberGenerator.html">Random Number Generator</A>
<LI>
<tt>RandomAccessIterator</tt>'s distance type is convertible to
<tt>RandomNumberGenerator</tt>'s argument type.
</UL>
<h3>Preconditions</h3>
<UL>
<LI>
<tt>[first, last)</tt> is a valid range.
<LI>
<tt>last - first</tt> is less than <tt>rand</tt>'s maximum value.
</UL>
<h3>Complexity</h3>
Linear in <tt>last - first</tt>. If <tt>last != first</tt>, exactly <tt>(last - first) -
1</tt> swaps are performed.
<h3>Example</h3>
<pre>
const int N = 8;
int A[] = {1, 2, 3, 4, 5, 6, 7, 8};
random_shuffle(A, A + N);
<A href="copy.html">copy</A>(A, A + N, <A href="ostream_iterator.html">ostream_iterator</A><int>(cout, " "));
// The printed result might be 7 1 6 3 2 5 4 8,
// or any of 40,319 other possibilities.
</pre>
<h3>Notes</h3>
<P><A name="1">[1]</A>
This algorithm is described in section 3.4.2 of Knuth
(D. E. Knuth, <i>The Art of Computer
Programming. Volume 2: Seminumerical Algorithms</i>, second edition.
Addison-Wesley, 1981). Knuth
credits Moses and Oakford (1963) and Durstenfeld (1964). Note that
there are N! ways of arranging a sequence of N elements. <tt>Random_shuffle</tt>
yields uniformly distributed results; that is, the probability of any
particular ordering is 1/N!. The reason this comment is important is
that there are a number of algorithms that seem at first sight to
implement random shuffling of a sequence, but that do not in fact
produce a uniform distribution over the N! possible orderings. That
is, it's easy to get random shuffle wrong.
<h3>See also</h3>
<tt><A href="random_sample.html">random_sample</A></tt>,
<tt><A href="random_sample_n.html">random_sample_n</A></tt>,
<tt><A href="next_permutation.html">next_permutation</A></tt>,
<tt><A href="prev_permutation.html">prev_permutation</A></tt>,
<A href="RandomNumberGenerator.html">Random Number Generator</A>
<!--start footer-->
<HR SIZE="6">
<A href="http://www.sgi.com/"><IMG SRC="surf.gif" HEIGHT="54" WIDTH="54"
ALT="[Silicon Surf]"></A>
<A HREF="index.html"><IMG SRC="stl_home.gif"
HEIGHT="54" WIDTH="54" ALT="[STL Home]"></A>
<BR>
<FONT SIZE="-2">
<A href="http://www.sgi.com/Misc/sgi_info.html" TARGET="_top">Copyright ©
1999 Silicon Graphics, Inc.</A> All Rights Reserved.</FONT>
<FONT SIZE="-3"><a href="http://www.sgi.com/Misc/external.list.html" TARGET="_top">TrademarkInformation</A>
</FONT>
<P>
</BODY>
</HTML>
|
