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| <TITLE>random_shuffle()</TITLE> |
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| <H2>random_shuffle()</H2> |
| <P><B>Library:</B> <A HREF="2-9.html">Algorithms</A></P> |
| |
| <PRE><HR><B><I>Function</I></B><HR></PRE> |
| |
| <UL> |
| <LI><A HREF="#sec1">Local Index</A></LI> |
| <LI><A HREF="#sec2">Summary</A></LI> |
| <LI><A HREF="#sec3">Synopsis</A></LI> |
| <LI><A HREF="#sec4">Description</A></LI> |
| <LI><A HREF="#sec5">Complexity</A></LI> |
| <LI><A HREF="#sec6">Example</A></LI> |
| <LI><A HREF="#sec7">Standards Conformance</A></LI> |
| </UL> |
| <A NAME="sec1"><H3>Local Index</H3></A> |
| No Entries |
| <A NAME="sec2"><H3>Summary</H3></A> |
| <P>Algorithm that randomly shuffles elements of a collection</P> |
| <A NAME="sec3"><H3>Synopsis</H3></A> |
| |
| <PRE>#include <algorithm> |
| |
| namespace std { |
| template <class RandomAccessIterator> |
| void random_shuffle(RandomAccessIterator start, |
| RandomAccessIterator finish); |
| |
| template <class RandomAccessIterator, |
| class RandomNumberGenerator> |
| void random_shuffle(RandomAccessIterator start, |
| RandomAccessIterator finish, |
| RandomNumberGenerator& rand); |
| } |
| </PRE> |
| <A NAME="sec4"><H3>Description</H3></A> |
| <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> |
| <A NAME="sec5"><H3>Complexity</H3></A> |
| <P>In the <SAMP>random_shuffle()</SAMP> algorithm, <SAMP>(finish - start) - 1 </SAMP>swaps are done.</P> |
| <A NAME="sec6"><H3>Example</H3></A> |
| |
| <UL><PRE>// |
| // rndshufl.cpp |
| // |
| |
| #include <algorithm> // for random_shuffle |
| #include <iostream> // for cout, endl |
| #include <iterator> // for ostream_iterator |
| #include <string> // for string |
| |
| |
| |
| int main () |
| { |
| // Create a string of doubles (unusual? maybe, |
| // but why not...) |
| typedef std::basic_string<double, |
| std::char_traits<double>, |
| std::allocator<double> > |
| Bizarre; |
| |
| // Initialize a Bizarre with an array of values. |
| const Bizarre::value_type a[] = { 1, 2, 3, 4, 5, |
| 6, 7, 8, 9, 10 }; |
| |
| Bizarre b (a + 0, a + sizeof a / sizeof *a); |
| |
| typedef std::ostream_iterator<double, char, |
| std::char_traits<char> > |
| Iter; |
| |
| // Suppress decimal point in output. |
| std::cout.precision (0); |
| |
| // Print out elements in original (sorted) order. |
| std::cout << "Elements before random_shuffle: \n "; |
| std::copy (b.begin (), b.end (), Iter (std::cout," ")); |
| |
| // Mix them up with random_shuffle. |
| std::random_shuffle (b.begin (), b.end ()); |
| |
| // Print out the mixed up elements. |
| std::cout << "\n\nElements after random_shuffle: \n "; |
| std::copy (b.begin (), b.end (), Iter (std::cout, " ")); |
| std::cout << std::endl; |
| |
| return 0; |
| } |
| |
| |
| Program Output: |
| </PRE></UL> |
| <UL><PRE>Elements before random_shuffle: |
| 1 2 3 4 5 6 7 8 9 10 |
| |
| Elements after random_shuffle: |
| 9 8 7 6 2 3 1 4 5 10 |
| </PRE></UL> |
| <A NAME="sec7"><H3>Standards Conformance</H3></A> |
| <P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems --Programming Language C++, Section 25.2.11</I></P> |
| |
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