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<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. 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It is provided "as is" without express or implied warranty. -- --><Head><Title>random_shuffle</Title><!-- Generated by htmldoc --></HEAD><BODY TEXT="#000000" LINK="#006600" ALINK="#003300" VLINK="#7C7F87" BGCOLOR="#FFFFFF"><A HREF="/"><IMG SRC="/images/common/sgilogo_small.gif" ALT="SGI Logo" WIDTH="80" HEIGHT="72" BORDER="0"></A><P><!--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> possibleorderings, 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 randomnumber 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 nonstandardbackward-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 ComputerProgramming. Volume 2: Seminumerical Algorithms</i>, second edition. Addison-Wesley, 1981). Knuthcredits 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 anyparticular 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 factproduce a uniform distribution over the N! possible orderings. Thatis, 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 --><!-- Footer Begins --><STYLE TYPE="text/css"><!--TD.footer, TD.footer A{ font-family: Arial, helvetica, sans-serif; font-size: 8pt;}A.home {font-family: Arial, helvetica, sans-serif;}--></STYLE><P><A CLASS="home" HREF="index.html">STL Home</A><P><TABLE WIDTH="600" CELLPADDING="0" CELLPADDING="0" BORDER="0"> <TR> <TD ALIGN="RIGHT" CLASS="footer"><A HREF="/company_info/terms.html" TARGET="_top">terms of use</A> | <A HREF="/company_info/privacy.html" TARGET="_top">privacy policy</A></TD> <TD ALIGN="CENTER" CLASS="footer"> | </TD> <TD ALIGN="LEFT" CLASS="footer"><A HREF="/cgi-bin/feedback/" TARGET="_top">contact us</A></TD> </TR><TR> <TD ALIGN="RIGHT" CLASS="footer">Copyright © 1993-2003 Silicon Graphics, Inc. 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