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142 lines
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<HTML>
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<HEAD>
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<TITLE>random_shuffle()</TITLE>
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<LINK REL=StyleSheet HREF="../rw.css" TYPE="text/css" TITLE="Apache stdcxx Stylesheet"></HEAD>
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<BODY BGCOLOR=#FFFFFF>
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<A HREF="randomaccessiterators.html"><IMG SRC="images/bprev.gif" WIDTH=20 HEIGHT=21 ALT="Previous file" BORDER=O></A><A HREF="noframes.html"><IMG SRC="images/btop.gif" WIDTH=56 HEIGHT=21 ALT="Top of Document" BORDER=O></A><A HREF="booktoc.html"><IMG SRC="images/btoc.gif" WIDTH=56 HEIGHT=21 ALT="Contents" BORDER=O></A><A HREF="tindex.html"><IMG SRC="images/bindex.gif" WIDTH=56 HEIGHT=21 ALT="Index page" BORDER=O></A><A HREF="range-error.html"><IMG SRC="images/bnext.gif" WIDTH=25 HEIGHT=21 ALT="Next file" BORDER=O></A><DIV CLASS="DOCUMENTNAME"><B>Apache C++ Standard Library Reference Guide</B></DIV>
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<H2>random_shuffle()</H2>
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<P><B>Library:</B> <A HREF="2-9.html">Algorithms</A></P>
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<PRE><HR><B><I>Function</I></B><HR></PRE>
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<UL>
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<LI><A HREF="#sec1">Local Index</A></LI>
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<LI><A HREF="#sec2">Summary</A></LI>
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<LI><A HREF="#sec3">Synopsis</A></LI>
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<LI><A HREF="#sec4">Description</A></LI>
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<LI><A HREF="#sec5">Complexity</A></LI>
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<LI><A HREF="#sec6">Example</A></LI>
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<LI><A HREF="#sec7">Standards Conformance</A></LI>
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</UL>
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<A NAME="sec1"><H3>Local Index</H3></A>
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No Entries
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<A NAME="sec2"><H3>Summary</H3></A>
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<P>Algorithm that randomly shuffles elements of a collection</P>
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<A NAME="sec3"><H3>Synopsis</H3></A>
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<PRE>#include <algorithm>
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namespace std {
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template <class RandomAccessIterator>
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void random_shuffle(RandomAccessIterator start,
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RandomAccessIterator finish);
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template <class RandomAccessIterator,
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class RandomNumberGenerator>
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void random_shuffle(RandomAccessIterator start,
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RandomAccessIterator finish,
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RandomNumberGenerator& rand);
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}
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</PRE>
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<A NAME="sec4"><H3>Description</H3></A>
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<P>The <SAMP>random_shuffle()</SAMP> algorithm shuffles the elements in the range <SAMP>[start, finish)</SAMP> with uniform distribution. <SAMP>random_shuffle()</SAMP> can take a particular random number generating function object <SAMP>rand</SAMP> (where <SAMP>rand</SAMP> takes a positive argument <SAMP>n</SAMP> of type convertible from <SAMP>std::iterator_traits<RandomAccessIterator>::difference_type</SAMP>) and returns a randomly chosen value between <SAMP>0 </SAMP>and<SAMP> n - 1</SAMP>. </P>
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<A NAME="sec5"><H3>Complexity</H3></A>
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<P>In the <SAMP>random_shuffle()</SAMP> algorithm, <SAMP>(finish - start) - 1 </SAMP>swaps are done.</P>
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<A NAME="sec6"><H3>Example</H3></A>
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<UL><PRE>//
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// rndshufl.cpp
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//
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#include <algorithm> // for random_shuffle
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#include <iostream> // for cout, endl
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#include <iterator> // for ostream_iterator
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#include <string> // for string
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int main ()
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{
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// Create a string of doubles (unusual? maybe,
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// but why not...)
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typedef std::basic_string<double,
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std::char_traits<double>,
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std::allocator<double> >
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Bizarre;
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// Initialize a Bizarre with an array of values.
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const Bizarre::value_type a[] = { 1, 2, 3, 4, 5,
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6, 7, 8, 9, 10 };
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Bizarre b (a + 0, a + sizeof a / sizeof *a);
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typedef std::ostream_iterator<double, char,
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std::char_traits<char> >
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Iter;
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// Suppress decimal point in output.
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std::cout.precision (0);
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// Print out elements in original (sorted) order.
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std::cout << "Elements before random_shuffle: \n ";
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std::copy (b.begin (), b.end (), Iter (std::cout," "));
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// Mix them up with random_shuffle.
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std::random_shuffle (b.begin (), b.end ());
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// Print out the mixed up elements.
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std::cout << "\n\nElements after random_shuffle: \n ";
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std::copy (b.begin (), b.end (), Iter (std::cout, " "));
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std::cout << std::endl;
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return 0;
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}
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Program Output:
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</PRE></UL>
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<UL><PRE>Elements before random_shuffle:
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1 2 3 4 5 6 7 8 9 10
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Elements after random_shuffle:
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9 8 7 6 2 3 1 4 5 10
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</PRE></UL>
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<A NAME="sec7"><H3>Standards Conformance</H3></A>
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<P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems --Programming Language C++, Section 25.2.11</I></P>
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<BR>
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