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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>partial_sort</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>partial_sort</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>Partial_sort</tt> is an overloaded name; there are actually two <tt>partial_sort</tt>functions.<pre>template <class <A href="RandomAccessIterator.html">RandomAccessIterator</A>>void partial_sort(RandomAccessIterator first, RandomAccessIterator middle, RandomAccessIterator last);template <class <A href="RandomAccessIterator.html">RandomAccessIterator</A>, class <A href="StrictWeakOrdering.html">StrictWeakOrdering</A>>void partial_sort(RandomAccessIterator first, RandomAccessIterator middle, RandomAccessIterator last, StrictWeakOrdering comp);</pre> <h3>Description</h3><tt>Partial_sort</tt> rearranges the elements in the range <tt>[first, last)</tt> sothat they are partially in ascending order. Specifically, it placesthe smallest <tt>middle - first</tt> elements, sorted in ascending order,into the range <tt>[first, middle)</tt>. The remaining <tt>last - middle</tt>elements are placed, in an unspecified order, into the range <tt>[middle,last)</tt>. <A href="#1">[1]</A> <A href="#2">[2]</A><P>The two versions of <tt>partial_sort</tt> differ in how they define whether oneelement is less than another. The first version comparesobjects using <tt>operator<</tt>, and the second compares objects usinga <A href="functors.html">function object</A> <tt>comp</tt>.<P>The postcondition for the first version of <tt>partial_sort</tt> is asfollows. If <tt>i</tt> and <tt>j</tt> areany two valid iterators in the range <tt>[first, middle)</tt> such that <tt>i</tt>precedes <tt>j</tt>, and if <tt>k</tt> is a valid iterator in the range <tt>[middle,last)</tt>, then <tt>*j < *i</tt> and <tt>*k < *i</tt> will both be <tt>false</tt>. The corresponding postcondition for the second version of <tt>partial_sort</tt>is that <tt>comp(*j, *i)</tt> and <tt>comp(*k, *i)</tt>are both false. Informally, this postcondition means that the first <tt>middle - first</tt>elements are in ascending order and that none of the elements in<tt>[middle, last)</tt> is less than any of the elements in <tt>[first, middle)</tt>.<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>.<LI><tt>RandomAccessIterator</tt> is mutable.<LI><tt>RandomAccessIterator</tt>'s value type is <A href="LessThanComparable.html">LessThan Comparable</A>.<LI>The ordering relation on <tt>RandomAccessIterator</tt>'s value type is a <i>strict weak ordering</i>, as defined in the <A href="LessThanComparable.html">LessThan Comparable</A> requirements.</UL>For the second version:<UL><LI><tt>RandomAccessIterator</tt> is a model of <A href="RandomAccessIterator.html">Random Access Iterator</A>.<LI><tt>RandomAccessIterator</tt> is mutable.<LI><tt>StrictWeakOrdering</tt> is a model of <A href="StrictWeakOrdering.html">Strict Weak Ordering</A>.<LI><tt>RandomAccessIterator</tt>'s value type is convertible to <tt>StrictWeakOrdering</tt>'s argument type.</UL><h3>Preconditions</h3><UL><LI><tt>[first, middle)</tt> is a valid range.<LI><tt>[middle, last)</tt> is a valid range.</UL>(It follows from these two conditions that <tt>[first, last)</tt> is a valid range.)<h3>Complexity</h3>Approximately <tt>(last - first) * log(middle - first)</tt> comparisons.<h3>Example</h3><pre>int A[] = {7, 2, 6, 11, 9, 3, 12, 10, 8, 4, 1, 5};const int N = sizeof(A) / sizeof(int);partial_sort(A, A + 5, A + N);copy(A, A + N, ostream_iterator<int>(cout, " "));// The printed result is "1 2 3 4 5 11 12 10 9 8 7 6".</pre><h3>Notes</h3><P><A name="1">[1]</A>Note that the elements in the range <tt>[first, middle)</tt> will be thesame (ignoring, for the moment, equivalent elements) as if you had sortedthe entire range using <tt>sort(first, last)</tt>. The reason for using<tt>partial_sort</tt> in preference to <tt>sort</tt> is simply efficiency: a partialsort, in general, takes less time.<P><A name="2">[2]</A><tt>partial_sort(first, last, last)</tt> has the effect of sorting theentire range <tt>[first, last)</tt>, just like <tt><A href="sort.html">sort</A>(first, last)</tt>. Theyuse different algorithms, however: <tt>sort</tt> uses the <i>introsort</i> algorithm(a variant of quicksort), and <tt>partial_sort</tt> uses <i>heapsort</i>. See section 5.2.3 ofKnuth (D. E. Knuth, <i>The Art of ComputerProgramming. Volume 3: Sorting and Searching</i>.Addison-Wesley, 1975.), and J. W. J. Williams (<i>CACM</i> <b>7</b>, 347, 1964).Both heapsort and introsort have complexity of order <tt>Nlog(N)</tt>, but introsort is usually faster by a factor of 2 to 5.<h3>See also</h3><tt><A href="partial_sort_copy.html">partial_sort_copy</A></tt>,<tt><A href="sort.html">sort</A></tt>,<tt><A href="stable_sort.html">stable_sort</A></tt>,<tt><A href="binary_search.html">binary_search</A></tt>,<tt><A href="lower_bound.html">lower_bound</A></tt>,<tt><A href="upper_bound.html">upper_bound</A></tt>,<tt><A href="less.html">less</A><T></tt>,<A href="StrictWeakOrdering.html">StrictWeakOrdering</A>,<A href="LessThanComparable.html">LessThan Comparable</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> ⌨️ 快捷键说明
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